SOLUTION: sqrtof 9x+81=x+5 not sure how to solve...please help

Question 167316: sqrtof 9x+81=x+5
not sure how to solve...please help
Found 2 solutions by jim_thompson5910, ankor@dixie-net.com:
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Start with the given equation

Square both sides to get rid of the square root.

FOIL

Subtract 9x from both sides. Subtract 81 from both sides.

Combine like terms.

Notice we have a quadratic equation in the form of where , , and

Let's use the quadratic formula to solve for x

Start with the quadratic formula

Plug in , , and

Square to get .

Multiply to get

Rewrite as

Add to to get

Multiply and to get .

Take the square root of to get .

or Break up the expression.

or Combine like terms.

or Simplify.

So the possible answers are or

However, if you plug in , then the equation won't be true.

=============================================

Answer:

So the only solution is
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
= x + 5
Square both sides:
9x + 81 = (x + 5)^2
:
FOIL the right side
9x + 81 = x^2 + 10x + 25
:
0 = x^2 + 10x - 9x + 25 - 81
:
A quadratic equation:
x^2 + x - 56 = 0
Factors to:
(x+8)(x-7) = 0
Two solutions
x = -8
and
x = 7
:
Both solutions have to be checked in the original equation:
x= -8
= -8 + 5
= -8 + 5
= -3
3 does not = -3; x = -8 is not a solution
:
x=+7
= 7 + 5
= 12
= 12
12 = 12; x=7 is good solution

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