Core Connections Geometry, 2013
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Core Connections Geometry, 2013 View details
1. Section 9.1
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Exercise 60 Page 551

Practice makes perfect
a To solve an equation, we first gather all of the variable terms on one side and all of the constant terms on the other side using the Properties of Equality. In this case, we will start by using the Distributive Property to simplify the left-hand side of the equation.
20 - 6(5+2x) = 10-2x
20 - 30 -12x = 10-2x
-10-12x = 10-2x
Now, we can continue to solve using the Properties of Equality.
-10-12x = 10-2x
â–Ľ
Solve for x
-10 = 10+10x
-20 = 10x
-2 = x
x= -2
The solution to the equation is x=-2.

Checking Our Answer

We can check our answer by substituting it back into the original equation. If simplifying the equation results in a true statement, we will know that our answer is correct. Let's do it!
20 - 6(5+2x) = 10-2x
20 - 6(5+2( -2)) ? = 10-2( -2)
20 - 6(5-4) ? = 10+4
20-6(1)? = 14
20-6? = 14
14 = 14 âś“
Since the left-hand side is equal to the right-hand side, our solution is correct.
b Let's use the Quadratic Formula to solve the given quadratic equation.
ax^2+ bx+ c=0 ⇕ x=- b± sqrt(b^2-4 a c)/2 a Since the equation is already written in the correct form, we can identify the values of a, b, and c. 2x^2-9x-5=0 ⇕ 2x^2+( - 9)x+( - 5)=0We see that a= 2, b= - 9, and c= - 5. Let's substitute these values into the Quadratic Formula.
x=- b±sqrt(b^2-4ac)/2a
x=- ( -9)±sqrt(( - 9)^2-4( 2)( - 5))/2( 2)
â–Ľ
Solve for x
x=9±sqrt((- 9)^2-4(2)(- 5))/2(2)
x=9±sqrt(81-4(2)(- 5))/2(2)
x=9±sqrt(81+40)/4
x=9±sqrt(121)/4
x = 9 ± 11/4
The solutions for this equation are x = 9 ± 114. Let's separate them into the positive and negative cases.
x = 9 ± 11/4
x_1 = 9 + 11/4 x_2 = 9 - 11/4
x_1=20/4 x_2=-2/4
x_1=5 x_2=-0.5

Using the Quadratic Formula, we found that the solutions of the given equation are x_1=5 and x_2=-0.5.

Checking Our Answers

In order to check whether our solutions are correct, let's substitute them into the original equation, starting with x=5.
2x^2-9x-5=0
2( 5)^2-9( 5)-5 ? = 0
2(25)-9(5)-5 ? = 0
50-45-5? = 0
0=0 âś“
Since the left-hand side is equal to the right-hand side, our solution is correct. Now let's substitute x=-0.5 into the equation and simplify.
2x^2-9x-5=0
2( -0.5)^2-9( -0.5)-5 ? = 0
2(0.25)-9(-0.5)-5 ? = 0
0.5+4.5-5? = 0
0=0 âś“
Again, since the left-hand side is equal to the right-hand side, our solution is correct.
c To solve the proportion, we will start by using the Cross Products Property. Remember that we will need to treat both the 5x-1 and x+1 as single quantities in the cross multiplication process.
3/5x-1=1/x+1 ⇔ 3(x+1)=5x-1 From here, we will continue solving for x by using the Distributive Property and the Properties of Equality.
3(x+1)=5x-1
3x+3 = 5x-1
â–Ľ
Solve for x
3 = 2x -1
4 = 2x
2 = x
x= 2
The solution is x = 2.

Checking Our Answer

Notice that we have x-terms in the denominators of our proportion. When solving this type equation, it is important to check for extraneous solutions. We can do so by substituting our solution into the original equation and simplifying. If the result is a true statement, our answer is correct.
3/5x-1=1/x+1
3/5( 2)-1? =1/2+1
3/10-1? =1/3
3/9? =1/3
1/3=1/3 âś“
Since the left-hand side is equal to the right-hand side, our solution is correct.
d An absolute value measures an expression's distance from zero on a number line.
|2x-1|= 5 This equation means that the distance is 5, either in the positive direction or the negative direction. |2x-1|= 5 ⇒ l2x-1= 5 2x-1= - 5 To find the solutions to the absolute value equation, we need to solve both of these cases for x.
| 2x-1|=5

lc 2x-1 ≥ 0:2x-1 = 5 & (I) 2x-1 < 0:2x-1 = - 5 & (II)

lc2x-1=5 & (I) 2x-1=- 5 & (II)

(I), (II): LHS+1=RHS+1

l2x=6 2x=- 4

(I), (II): .LHS /2.=.RHS /2.

lx_1=3 x_2=- 2
Both 3 and -2 are solutions to the absolute value equation.

Checking Our Answers

When solving an absolute value equation, it is important to check for extraneous solutions. We can check our answers by substituting them back into the original equation. Let's start with x=3.
|2x-1|=5
|2( 3)-1|? =5
|6-1|? =5
|5|? =5
5 = 5 âś“
We will check x=-2 in the same way.
|2x-1|=5
|2( -2)-1|? =5
|-4-1|? =5
|-5|? =5
5 = 5 âś“
We see that both solutions satisfy the original equation.