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More Algebra! Oh no!

# More Algebra! Oh no!. Examples: 6 * 3 = 18, positive * positive = positive -8 * 5 = -40, negative * positive = negative -7.5 * -2.8 = 21, negative * negative

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### Text of More Algebra! Oh no!. Examples: 6 * 3 = 18, positive * positive = positive -8 * 5 = -40, negative *...

• More Algebra! Oh no!

• Examples:

6 * 3 = 18, positive * positive = positive

-8 * 5 = -40, negative * positive = negative

-7.5 * -2.8 = 21, negative * negative = positive

• Practice:

-12 * 5 =

-3.2 * -28 =

-3 * 5 * (-14) =

_4 =

-6 =

• Practice:

-12 * 5 = -60

-3.2 * -28 = 89.6

-3 * 5 * (-14) = 210

_4 = (-4 * -4) = 16

-6 = (-6 * -6 * -6) = -216

• Evaluate 3x2 when x = 4 and x = -4.

3(4) 3(16) 48

3(-4) 3(16) 48

• Same as multiplication! Duh!

• Addition: For any numbers a, and b,a + b = b + a.(We can change the order when adding without affecting the answer.)Multiplication. For any numbers a and b,ab = ba(We can change the order when multiplying without affecting the answer.)The Commutative Laws

• Evaluate xy and yx when x = 7 and y = -5.

SolutionWe substitute 7 for x and -5 for y.xy = 7(-5) = -35

yx = -5(7) = -35

• Addition: For any numbers a, b, and c,a + (b + c) = (a + b) + c.(Numbers can be grouped in any manner for addition.)Multiplication. For any numbers a, b, and c,a * (b * c) = (a * b) * c(Numbers can be grouped in any manner for multiplication.)The Associative Laws

• Calculate and compare:4 + (9 + 6) and (4 + 9) + 6.

4 + 15 13 + 619 19

• For any numbers a, b, and c,a(b + c) = ab + ac.The Distributive Law of Multiplication over Addition For any numbers a, b, and c,a(b c) = ab - ac.The Distributive Law of Multiplication over Subtraction

• Multiply.

4(a + b).

4 * a + 4 * b4a + 4b

• Practice:Multiply. 8(a b) (b 7)c 5(x 3y + 2z)

• Practice:Multiply. 8(a b) = 8a 8b (b 7)c = bc 7c 5(x 3y + 2z) = -5x + 15y 10z

• Factoring is the reverse of multiplying. To factor, we can use the distributive laws in reverse:ab + ac = a(b + c) and ab ac = a(b c).

To factor an expression is to find an equivalent expression that is a product. Factoring

• Factor.a.6x 12 b. 8x + 32y 8

a.6x 126 * x 6 * 26(x 2)8x + 32y - 88 * x + 8 * 4 * y 88(x + 4y 8)

• Practice:Factor. a. 7x 7y b. 14z 12x 20

• Practice:Factor. a. 7x 7y 7 * x 7* y 7(x y)b. 14z 12x 20 2 * 7z 2 * 6x 2 * 10 2(7z 6x 10)

• When the variable is exactly the same then the terms can be combined:2x + 4x = 6xIf the variables are different or have a different exponent then they cannot be combined2x + 4y, cannot be combined3m + 5m, cannot be combined

• Examples:

3x + 2 6x + y3x 6x + 2 + y-3x + 2 + y

2x - 5 + 9x + 23 8x +3x2x - 8x + 9x + 3x 5 + 23-6x + 12x + 186(-x + 2x + 3)

• EquationAn equation is a number sentence that says that the expressions on either side of the equals sign, =, represent the same number.

• 9 + 8x = 3

We need to isolate x to solve the equation. We have been doing this all term. What do we do first?

• 9 + 8x = 3

First, we get rid of the 9

9 + 8x - 9 = 3 98x = -6

Now what?

• 8x = -6

Remember that 8x just means 8 * x, so we need to get rid of the 8:

8x/8 = -6/8x = -6/8 Dont forget to reducex = -3/4

9 + 8x = 3x = -3/49 + 8(-3/4) = 39 - 24/4 = 39 6 = 33 = 3Our answer is correct!

• Lets try another:5x + 4x = 36

Here we need to combine like terms. That means anything with the same variable next to it can be added together:5x + 4x = 369x = 369x/9 = 36/9x = 4Remember to always check you answer:5x + 4x = 365(4) + 4(4) = 3620 + 16 = 3636 = 36

• Here is a toughie!

4x + 7 6x = 10 +3x + 12

Holy cow! What do we do with this?!

• 4x + 7 6x = 10 +3x + 12

First, we combine like terms:4x + 7 6x = 10 + 3x + 127 2x = 3x + 22Now we need to get both xs on the same side and finish:7 2x + 2x = 3x + 22 + 2x7 = 5x + 227 22 = 5x + 22 -22-15 = 5x-15/5 = 5x/5-3 = x

• Always check the answer:4x + 7 6x = 10 + 3x + 124(-3) + 7 6(-3) = 10 + 3(-3) + 12-12 + 7 + 18 = 10 9 + 12-5 + 18 = 1 + 1213 = 13

Correct!

• Slide 8- *Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-WesleyAn Equation-Solving Procedure1. Multiply on both sides to clear the equation of fractions or decimals. (This is optional, but can ease computations.) Not a fan of this one.2.If parentheses occur, multiply to remove them using the distributive laws.3.Collect like terms on each side, if necessary.4.Get all terms with variables on one side and all numbers (constant terms) on the other side, using the addition principle. 5.Collect like terms again, if necessary. 6.Multiply or divide to solve for the variable, using the multiplication principle.7.Check all possible solutions in the original equation.

• 3 8(x + 6) = 4(x 1) 5Oh no! Parentheses! Be afraid, be very afraid! (Not really)

What do we do first to get rid of the parentheses?

• 3 8(x + 6) = 4(x 1) 5Thats right! Use the distributive property of multiplication:3 8x - 48 = 4x 4 5Now we just do the regular stuff:-8x - 45 = 4x 9-8x - 45 -4x = 4x 9 -4x-12x - 45 = -9-12x - 45 + 45 = -9 + 45-12x = 36-12x/-12 = 36/-12x = -3

• Check our answer:3 8(x + 6) = 4(-3 1) 53 8(-3 + 6) = 4(-3 1) 53 8(3) = 4(-4) 53 24 = -16 5-21 = -21

Got it!

• Formulas are often composed of multiple variables. It is important to know how to change the equation around to solve for the unknown variable:d = r * t, d is distance, r is rate, and t is time

Suppose we know the t and distance. Lets change the equation to solve for r:d/t = r * t / td/t = r or r = d/tSee?

• To solve a problem involving percents, it is helpful to translate first to an equation. For example, 23% of 5 is what?

23% of 5 is what? 0.23 * 5 = a

• What is 19% of 82?

This is a reverse version of the previous example:Amount = Percent number * Base orPercent number * Base = Amount19% * 82 = x.19 * 82 = x15.58 = x

• 15 is 16% of what?Amount = percent * base15 = 16% * n15 = .16 * n15/.16 = .16/.16 * n93.75 = n

Check answer:15 = 16% * 93.7515 = .16 * 93.7515 = 15

• 27 is what percent of 36?Amount = percent * base27 = v * 3627/36 = v * 36/36.75 = v75% = v

Check answer:27 = 75% * 3627 = .75 * 3627 = 27

• Five Steps for Problem Solving in Algebra1. Familiarize yourself with the problem situation.2. Translate the problem to an equation.3. Solve the equation.4. Check the answer in the original problem.5. State the answer to the problem clearly.

• Digicon prints digital photos for \$0.12 each plus \$3.29 shipping and handling. Your weekly budget for the school yearbook is \$22.00. How many prints can you have made if you have \$22.00?

We first need to make an equation. Lets use n for the number of prints we can make..12 * n is the cost per picture.We need to add 3.29 for shipping, so we have:(.12 * n) + 3.29 = cost of pictures

• Digicon prints digital photos for \$0.12 each plus \$3.29 shipping and handling. Your weekly budget for the school yearbook is \$22.00. How many prints can you have made if you have \$22.00?

We know that we can only spend \$22, so that is our total cost:(.12 * n) + 3.29 = 22This is our equation.

• Now that we have our equation, we just solve for our variable:(.12 * n) + 3.29 = 22.12n + 3.29 3.29 = 22 -3.29.12n = 18.71.12n/.12 = 18.71/.12n = 155.916666

Remember that our answer needs to be in number of pictures, so the most pictures we can develop in one week is 155.

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