Pearson Algebra 1 Common Core, 2011
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Exercise 19 Page 661

Raise both sides of the equation to a power equal to the index of the radical.

1

Practice makes perfect

Let's start by replacing the variable b with the variable x. 2b=sqrt(b+3) b= x ⟶ 2 x=sqrt(x+3) Since the radical is isolated, we can raise both sides of the equation to a power equal to the index of the radical. Let's try to solve our equation using this method!

2x=sqrt(x+3)
(2x)^2=(sqrt(x+3))^2
2^2x^2=(sqrt(x+3))^2
4x^2=(sqrt(x+3))^2
4x^2=x+3
â–¼
LHS-(x+3)=RHS-(x+3)
4x^2-x=3
4x^2-x-3=0
We now have a quadratic equation, and we need to find its roots. To do it, let's identify the values of a, b, and c. 4x^2-x-3 = 0 ⇕ 4x^2+( -1)x+( -3)=0 We can see that a= 4, b= -1, and c= -3. Let's substitute these values into the Quadratic Formula.

x=- b±sqrt(b^2-4ac)/2a
x=- ( -1)±sqrt(( -1)^2-4( 4)( -3))/2( 4)
â–¼
Solve for x and Simplify
x=1±sqrt((-1)^2-4(4)(-3))/2(4)
x=1±sqrt(1^2-4(4)(-3))/2(4)
x=1±sqrt(1-4(4)(-3))/2(4)
x=1±sqrt(1+48)/8
x=1±sqrt(49)/8
x=1± 7/8

Using the Quadratic Formula, we found that the solutions of the given equation are x= 1±78.

x=1± 7/8
x_1=1+7/8 x_2=1-7/8
x_1=8/8 x_2=-6/8
x_1= 1 x_2= -3/4

Therefore, the solutions are x_1= 1 and x_2= - 34. Recall that, at the beginning of the solution, we substituted x for b. Consequently, the solutions to the original equation are b_1= 1 and b_2= - 34. Let's check them to see if we have any extraneous solutions.

Checking the Solutions

We will check b_1=1 and b_2=- 34 one at a time.

b_1=1

Let's substitute b= 1 into the original equation.

2b=sqrt(b+3)
2( 1)? =sqrt(1+3)
â–¼
Simplify
2? =sqrt(1+3)
2? =sqrt(4)
2 = 2 ✓

We got a true statement. Therefore, b=1 is a solution of the original equation.

b_2=-3/4

Now, let's substitute b= - 34.

2b=sqrt(b+3)
2( -3/4)? =sqrt(-3/4+3)
â–¼
Simplify
2(-3/4)? =sqrt(-3/4+3)
2(-3)/4? =sqrt(-3/4+3)
-2*3/4? =sqrt(-3/4+3)
-6/4? =sqrt(-3/4+3)
-6/4? =sqrt(-3/4+3)
-3/2? =sqrt(-3/4+3)
-3/2? =sqrt(-3/4+12/4)
-3/2? =sqrt(12/4-3/4)
-3/2? =sqrt(12-3/4)
-3/2? =sqrt(9/4)
-3/2 ≠ 3/2 *

In this case, we got a false statement, so b=-3/4 is an extraneous solution. Therefore, b=1 is the only solution of the original equation.