Core Connections Algebra 2, 2013
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Core Connections Algebra 2, 2013 View details
3. Section 8.3
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Exercise 174 Page 428

Practice makes perfect
a Before we can solve the given equation, we need to isolate the absolute value expression using the Properties of Equality.
2|x-3|+7 = 11
2|x-3| = 4
|x-3| = 2
An absolute value measures an expression's distance from a midpoint on a number line. |x-3| = 2 This equation means that the distance is 2, either in the positive direction or the negative direction. |x-3|= 2 ⇒ lx-3= 2 x-3= - 2 To find the solutions to the absolute value equation, we need to solve both of these cases for x.
| x-3|=2

lc x-3 ≥ 0:x-3 = 2 & (I) x-3 < 0:x-3 = - 2 & (II)

lcx-3=2 & (I) x-3=- 2 & (II)

(I), (II): LHS+3=RHS+3

lx_1=5 x_2=1
Both 5 and 1 are solutions to the absolute value equation.
b To solve the given quadratic equation, we can isolate the variable expression raised to the power of 2 and take the square roots. Remember to consider the positive and negative solutions.
4(x-2)^2 = 16
â–Ľ
Solve for x
(x-2)^2 = 4
sqrt((x-2)^2) = sqrt(4)
|x-2| = sqrt(4)
|x-2| = 2

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

x-2 = ± 2
x = ± 2 + 2
We found that x=± 2 + 2. We will now find both solutions by using the positive and negative signs.
x=± 2 + 2
x=2 + 2 x=-2 + 2
x=4 x=0

There are two solutions to the given equation, x=4 and x=0.

c To solve equations with a variable expression inside a radical, we first want to make sure the radical is isolated. Then we can raise both sides of the equation to a power equal to the index of the radical. Note that the square root in the given equation is already isolated.
sqrt(x+18) = x-2
( sqrt(x+18) )^2 = (x-2)^2
x+18 = (x-2)^2
â–Ľ
Solve for x
x+18 = x^2-2(x)(2)+2^2
x+18 = x^2-4x+2^2
x+18 = x^2-4x+4
18 = x^2-5x+4
0 = x^2-5x-14
x^2-5x-14 = 0
Note that we obtained a quadratic equation. To solve it we will use the Quadratic Formula. ax^2+ bx+ c=0 ⇕ x=- b± sqrt(b^2-4 a c)/2 aWe first need to identify the values of a, b, and c. x^2-5x-14=0 ⇕ 1x^2+( - 5)x+( -14)=0 We see that a= 1, b= - 5, and c= -14. Let's substitute these values into the Quadratic Formula.
x=- b±sqrt(b^2-4ac)/2a
x=- ( -5)±sqrt(( -5)^2-4( 1)( -14))/2( 1)
â–Ľ
Evaluate right-hand side
x=5±sqrt((- 5)^2-4(1)(-14))/2(1)
x=5±sqrt(25-4(1)(-14))/2(1)
x=5±sqrt(25-4(-14))/2
x=5±sqrt(25+56)/2
x=5±sqrt(81)/2
x=5± 9/2
Using the Quadratic Formula, we found that the solutions of the given equation are x= 5± 92.
x=5± 9/2
x_1=5+9/2 x_2=5-9/2
x_1=14/2 x_2=-4/2
x_1= 7 x_2= -2
The solutions are x_1=7 and x_2= -2. Finally, we will check for extraneous solutions by substituting both x= 7 and x= -2 into the original equation. Let's start with x= 7.
sqrt(x+18) = x-2
sqrt(7+18) ? = 7-2
â–Ľ
Simplify
sqrt(25) ? = 5
5=5 âś“
Since we obtained a true statement, x= 7 is indeed a solution to the original equation. Finally, let's check x= -2.
sqrt(x+18) = x-2
sqrt(-2+18) ? = -2-2
â–Ľ
Simplify
sqrt(16) ? = -4
4≠ -4 *
This time we obtained a false statement. Therefore, x= -2 is not a solution to the original equation.
d An absolute value measures an expression's distance from a midpoint on a number line.
|2x+5|= 3x+4 This equation means that the distance is 3x+4, either in the positive direction or the negative direction. |2x+5|= 3x+4 ⇓ l2x+5= (3x+4) 2x+5= -(3x+4) To find the solutions to the absolute value equation, we need to solve both of these cases for n.
lc2x+5=3x+4 & (I) 2x+5=-(3x+4) & (II)
â–Ľ
(I), (II): Solve for x
l2x+5=3x+4 2x+5=-3x-4

(I), (II): LHS-5=RHS-5

l2x=3x-1 2x=-3x-9
l0=x-1 2x=-3x-9
l0=x-1 5x=-9
l1=x 5x=-9
lx=1 5x=-9
lx=1 x= -95
lx=1 x=- 95
Both x=1 and x=- 95 are solutions to the equation. Finally, we will check for extraneous solutions by substituting both x=1 and x=- 95 into the original equation. Let's start with x=1.
|2x+5| = 3x+4
|2( 1)+5| ? = 3( 1)+4
â–Ľ
Simplify
|2+5| ? = 3+4
|7| ? = 7
7=7 âś“
Since we obtained a true statement, x=1 is indeed a solution to the original equation. Finally, let's check x=- 95.
|2x+5| = 3x+4
|2( -9/5)+5| ? = 3( -9/5)+4
â–Ľ
Simplify
|-2*9/5+5| ? = -3*9/5+4
|-18/5+5| ? = -27/5+4
|-18/5+25/5| ? = -27/5+20/5
|7/5| ? = -7/5
7/5≠ -7/5 *
This time we obtained a false statement. Therefore, x=- 95 is not a solution to the original equation.