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Misc. Algebra: You Know, Like Miss South Carolina

# Misc. Algebra: You Know, Like Miss South Carolina

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Part I: Pre-Calculus Review

9.

Does ^ a + b + c h equal a 4 + b 4 + c 4 ? Why or

why not?

4

Does

Solve It

Rewrite

3 4

x with a single radical sign.

Solve It

Solve It

11.

10.

a 2 + b 2 equal a + b ? Why or why not?

12.

Rewrite log a b = c as an exponential

equation.

Solve It

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Chapter 1: Getting Down the Basics: Algebra and Geometry

13.

Rewrite log c a - log c b with a single log.

Solve It

15.

If 5x 2 = 3x + 8 , solve for x with the

Solve It

14.

Rewrite log 5 + log 200 with a single log and

then solve.

Solve It

16.

Solve 3x + 2 > 14 .

Solve It

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Part I: Pre-Calculus Review

Geometry: When Am I Ever Going to Need It?

You can use calculus to solve many real-world problems that involve surfaces, volumes,

and shapes, such as maximizing the volume of a cylindrical soup can or determining

the stress along a cable hanging in a parabolic shape. So you’ve got to know the basic

geometry formulas for length, area, and volume. You also need to know basic stuff like

the Pythagorean Theorem, proportional shapes, and basic coordinate geometry like the

distance formula.

Q.

What’s the area of the triangle in the following figure?

x

Q.

How long is the hypotenuse of the triangle

in the previous example?

A.

x=4

a2 + b2 = c2

x 2 = a2 + b2

3

2

x 2 = 13 + 3

x 2 = 13 + 3

x 2 = 16

x=4

13

A.

2

39

2

Areatriangle = 1 base \$ height

2

1

= \$ 13 3

2

39

=

2

17.

Fill in the two missing lengths for the sides

of the triangle in the following figure.

18.

What are the lengths of the two missing

sides of the triangle in the following figure?

10

a

b

8

30˚

b

60˚

Solve It

a

Solve It

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Chapter 1: Getting Down the Basics: Algebra and Geometry

19.

Fill in the missing lengths for the sides of

the triangle in the following figure.

20.

a. What’s the total area of the pentagon in

the following figure?

b. What’s the perimeter?

60˚

6

b

10

45˚

60˚

a

Solve It

21.

Solve It

Compute the area of the parallelogram in

the following figure.

22.

What’s the slope of PQ?

y

(c,d) Q

4

45˚

10

Solve It

P

(a,b)

x

Solve It

13

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Part I: Pre-Calculus Review

23.

How far is it from P to Q in the figure from

problem 22?

Solve It

24.

What are the coordinates of the midpoint

of PQ in the figure from problem 22?

Solve It

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Chapter 1: Getting Down the Basics: Algebra and Geometry

Solutions for This Easy Elementary Stuff

a

Solve 5 = ? . 5 is undefined! Don’t mix this up with something like 0 , which equals zero. Note

8

0

0

5

that if you think about these two fractions as examples of slope ( rise

run ), 0 has a rise of 5 and a

run of 0 which gives you a vertical line that has sort of an infinite steepness or slope (that’s why

it’s undefined). Or just remember that it’s impossible to drive up a vertical road and so it’s

impossible to come up with a slope for a vertical line. The fraction 0 , on the other hand, has a

8

rise of 0 and a run of 8, which gives you a horizontal line that has no steepness at all and thus

has the perfectly ordinary slope of zero. Of course, it’s also perfectly ordinary to drive on a

b

0 = 0 (See solution to problem 1.)

10

+b

Does 3a + b equal a

a + c ? No. You can’t cancel the 3s.

3a + c

c

You can’t cancel in a fraction unless there’s an unbroken chain of multiplication running across

the entire numerator and ditto for the denominator.

d

e

Does 3a + b equal bc ? No. You can’t cancel the 3as. (See previous Warning.)

3a + c

4

Does ab equal ab

ac ? Yes. You can cancel the 4s because the entire numerator and the entire

4ac

denominator are connected with multiplication.

g

Does 4ab equal bc ? Yes. You can cancel the 4as.

4ac

Rewrite x - 3 without a negative power. 13

x

h

Does ^ abch equal a 4 b 4 c 4 ? Yes. Exponents do distribute over multiplication.

i

Does ^ a + b + c h equal a 4 + b 4 + c 4 ? No! Exponents do not distribute over addition

(or subtraction).

f

4

4

When you’re working a problem and can’t remember the algebra rule, try the problem with

numbers instead of variables. Just replace the variables with simple, round numbers and work

out the numerical problem. (Don’t use 0, 1, or 2 because they have special properties that can

mess up your example.) Whatever works for the numbers will work with variables, and whatever doesn’t work with numbers won’t work with variables. Watch what happens if you try this

problem with numbers:

^ 3 + 4 + 6h = 3 4 + 4 4 + 6 4

?

13 4 = 81 + 256 + 1296

28, 561 ! 1633

4 ?

j

Rewrite

k

Does a 2 + b 2 equal a + b ? No! The explanation is basically the same as for problem 9. Consider

1/2

this: If you turn the root into a power, you get a 2 + b 2 = _ a 2 + b 2 i . But because you can’t

3 4

x with a single radical sign.

3 4

x = 12 x

distribute the power, _ a 2 + b 2 i ! _ a 2 i + _ b 2 i , or a + b, and thus

1/2

1/2

1/2

l

Rewrite log a b = c as an exponential equation. a c = b

m

Rewrite log c a - log c b with a single log. log c a

b

a2 + b2 ! a + b.

15

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Part I: Pre-Calculus Review

n

Rewrite log 5 + log 200 with a single log and then solve. log 5 + log 200 = log ^ 5 \$ 200h = log 1000 = 3

When you see “log” without a base number, the base is 10.

o

If 5x 2 = 3x + 8 , solve for x with the quadratic formula. x = 8 or -1

5

Start by rearranging 5x 2 = 3x + 8 into 5x 2 - 3x - 8 = 0 because you want just a zero on one side

of the equation.

- b ! b 2 - 4ac

The quadratic formula tells you that x =

. Plugging 5 into a, –3 into b, and –8

2a

- ^ - 3 h ! ^ - 3 h - 4 ^ 5 h^ - 8 h 3 ! 9 + 160 3 ! 13 16

=

=

=

or - 10 ,

10

10

10

10

2\$5

2

into c gives you x =

so x = 8 or -1.

5

p

Solve 3x + 2 > 14 . x < - 16 , x > 4

3

1. Turn the inequality into an equation: 3x + 2 = 14

2. Solve the absolute value equation.

3x + 2 = 14

3x = 12

x=4

or

3x + 2 = -14

3x = -16

x = - 16

3

3. Place both solutions on a number line (see the following figure). (You use hollow dots for

> and <; if the problem had been \$ or #, you would use solid dots.)

-16

3

4

4. Test a number from each of the three regions on the line in the original inequality.

For this problem you can use –10, 0, and 10.

3 \$ ^ - 10h + 2 > 14

?

?

- 28 > 14

?

28 > 14

True, so you shade the left-most region.

3 \$ ^ 0 h + 2 > 14

?

?

2 > 14

False, so you don’t shade the middle region.

?

3 \$ 10 + 2 > 14

?

32 > 14

?

32 > 14

True, so shade the region on the right. The following figure shows the result. x can be any

-16

3

4

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Chapter 1: Getting Down the Basics: Algebra and Geometry

5. If it floats your boat, you may also want to express the answer symbolically.

Because x can equal a number in the left region or a number in the right region, this is an or

solution which means union ^ , h . When you want to include everything from both regions

on the number line, you want the union of the two regions. So, the symbolic answer is

x < - 16 , x > 4

3

If only the middle region were shaded, you’d have an and or intersection ^ + h problem. When

you only want the section of the number line where the two regions overlap, you use the intersection of the two regions. Using the above number line points, for example, you would write

the middle-region solution like

x < - 16 and x > 4 or

3

16

x< + x > 4 or

3

- 16 < x < 4

3

You say “to-may-to,” I say “to-mah-to.”

While we’re on the subject of absolute value, don’t forget that

equal ! x .

q

x2 = x .

x 2 does not

Fill in the two missing lengths for the sides of the triangle. a = 5 and b = 5 3

This is a 30°-60°-90° triangle — Well, duhh!

r

Fill in the two missing lengths for the sides of the triangle.

8 3

a = 8 or

3

3

16 3

b = 16 or

3

3

Another 30°-60°-90° triangle.

s

Fill in the two missing lengths for the sides of the triangle. a = 6 and b = 6 2

Make sure you know your 45°-45°-90° triangle.

t

25 3

a. What’s the total area of the pentagon? 50 +

.

2

10

10

by

The square is

(because half a square is a 45°-45°-90° triangle), so the area is

2

2

10 10 = 100 = 50 . The equilateral triangle has a base of 10 , or 5 2, so its height is 5 6

\$

2

2

2

2

2

(because half of an equilateral triangle is a 30°-60°-90° triangle). So the area of the triangle is

J

N

1 5 2 K 5 6 O = 25 12 = 50 3 = 25 3 . The total area is thus 50 + 25 3 .

`

jK

2

2 O

4

4

2

2

L

P

b. What’s the perimeter? The answer is 25.

The sides of the square are 10 , or 5 2, as are the sides of the equilateral triangle.

2

The pentagon has five sides, so the perimeter is 5 \$ 5 2, or 25 2 .

17

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Part I: Pre-Calculus Review

u

v

Compute the area of the parallelogram. The answer is 20 2.

The height is 4 , or 2 2 , because the height is one of the legs of a 45°-45°-90° triangle, and

2

the base is 10. So, because the area of a parallelogram equals base times height, the area is

10 \$ 2 2, or 20 2 .

rise y 2 - y 1

-b

What’s the slope of PQ? d

c - a . Remember that slope = run = x 2 - x 1 .

w

How far is it from P to Q? ^ c - ah + ^ d - b h

2

2

Remember that distance = _ x 2 - x 1i + _ y 2 - y 1i .

2

x

2

What are the coordinates of the midpoint of PQ? c a + c , b + d m . The midpoint of a segment is

2

2

given by the average of the two x coordinates and the average of the two y coordinates.

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Chapter 2

Funky Functions and Tricky Trig

In This Chapter

ᮣ Figuring functions

ᮣ Remembering Camp SohCahToa

I

n Chapter 2, you continue your pre-calc warm-up that you began in Chapter 1. If algebra is

the language calculus is written in, you might think of functions as the “sentences” of calculus. And they’re as important to calculus as sentences are to writing. You can’t do calculus

without functions. Trig is important not because it’s an essential element of calculus — you

could do most of calculus without trig — but because many calculus problems happen to

involve trigonometry.

To make a long story short, a function is basically anything you can graph on your graphing

calculator in “ y =” or graphing mode. The line y = 3x - 2 is a function, as is the parabola

y = 4x 2 - 3x + 6 . On the other hand, the sideways parabola x = 3y 2 - 4y + 6 isn’t a function

because there’s no way to write it as y = something. Try it.

You can determine whether or not the graph of a curve is a function with the vertical line test.

If there’s no place on the graph where you could draw a vertical line that touches the curve

more than once, then it is a function. And if you can draw a vertical line anywhere on the

graph that touches the curve more than once, then it is not a function.

As you know, you can rewrite the above functions using “f ^ x h ” or “ g ^ x h ” instead of “y.” This

changes nothing; using something like f ^ x h is just a convenient notation. Here’s a sampling

of calculus functions:

g l ^ x h = 3x 5 - 20x 3

f l ^ x h = lim

h"

0

x+hh

x

x

Af ^ xh =

# 10dt

3

Virtually every single calculus problem involves functions in one way or another. So should

you review some function basics? You betcha.

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Part I: Pre-Calculus Review

Q.

If f ^ x h = 3x 2 - 4x + 8 , what does f ^ a + b h

equal?

Q.

For the line g ^ x h = 5 - 4x , what’s the slope

and what’s the y-intercept?

A.

3a 2 + 6ab + 3b 2 - 4a - 4b + 8

A.

The slope is –4 and the y-intercept is 5.

Does y = mx + b ring a bell? It better!

2.

If the slope of line l is 3,

f ^ x h = 3x 2 - 4x + 8

f ^a + bh = 3 ^a + bh - 4 ^a + bh + 8

2

= 3 _ a 2 + 2ab + b 2 i - 4a - 4b + 8

= 3a 2 + 6ab + 3b 2 - 4a - 4b + 8

1.

Which of the four relations shown in the

figure represent functions and why? (A

relation, by the way, is any collection of

points on the x-y coordinate system.)

y

y

b. x 2 + y 2 = 9

a. y = |x|

y

y

x

x

c. x = y 3 - 5y 2 + 10

Solve It

d. y = sinx

b. What’s the slope of a line perpendicular

to l?

Solve It

x

x

a. What’s the slope of a line parallel to l?

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