Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
4. Solving Radical Equations and Inequalities
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Exercise 15 Page 266

Raise each side of the equation to a power equal to the index of the radical to eliminate the radical.

x=12

Practice makes perfect

Solving a radical equation usually involves three main steps.

  1. Isolate the radical on one side of the equation.
  2. Raise each side of the equation to a power equal to the index of the radical to eliminate the radical.
  3. Solve the resulting equation. Remember to check your results!
Now we can analyze the given radical equation. x-6=sqrt(3x)Notice that in this equation there is an isolated radical with index equal to 2 on the right-hand side. Then, we will raise each side of the equation to the power of 2.
x-6=sqrt(3x)
(x-6)^2=(sqrt(3x))^2
â–¼
Simplify
(x-6)^2=3x
x^2-2(x)(6)+6^2=3x
x^2-12x+6^2=3x
x^2-12x+36=3x
x^2-15x+36=0
We obtained a quadratic equation. There are many ways to solve a quadratic equation. We will use the Quadratic Formula to solve this equation. Let's determine a, b, and c. x^2-15x+36=0 ⇔ 1x^2+( -15)x+ 36=0 We see above that a= 1, b= -15, and c= 36. Let's substitute these values into the Quadratic Formula to solve the equation.
x=- b±sqrt(b^2-4ac)/2a
x=-( -15)±sqrt(( -15)^2-4( 1)( 36))/2( 1)
â–¼
Simplify right-hand side
x=15±sqrt((- 15)^2-4(1)(36))/2(1)
x=15±sqrt(225-4(1)(36))/2(1)
x=15±sqrt(225-144)/2
x=15±sqrt(81)/2
x=15± 9/2
Now we can calculate the first root using the positive sign and the second root using the negative sign.
x=15± 9/2
x=15+9/2 x=15-9/2
x=12 x=3

Checking the Solutions

Next, we will check the solutions by substituting 12 and 3 for x into the original equation. If the substitution produces a true statement, we know that our answer is correct. If it does not, then it is an extraneous solution. Let's first check the 12.
x-6=sqrt(3x)
12-6? =sqrt(3( 12))
â–¼
Simplify
12-6? =sqrt(36)
12-6? =6
6=6 ✓
Because our substitution produced a true statement, we know that our answer, x=12, is correct. Let's check now the 3.
x-6=sqrt(3x)
3-6? =sqrt(3( 3))
â–¼
Simplify
3-6? =sqrt(9)
3-6? =3
- 3≠ 3 *
Because our substitution produced a false statement, we know that our answer, x=3, is not correct.