Solving quadratic equation: x^2 + 20x = 125

[alee]

Solve for x: x^2 + 20x = 125

My solution was as follows, and was wrong:

. . .x^2 + 20X - 125 = 0
. . .(x + 25)(x - 5) - 125 = 0

. . .Therefore x = -25 and x = 5

Where did I go wrong? Thank you.

 

[Mrspi]

Re: equadtic equation

Solve for x x^2 + 20x = 125 my solution was as follows, and was wrong
x^2 +20X -125 = 0
(x+25)(x-5) -125 = 0<-----HERE is your mistake. (x + 25)(x - 5) - 125 is NOT the same thing as x^2 + 20x - 125
therefore x = -25 and x = 5 where did I go wrong? Thankyou

When you are at this point,
x^2 + 20x - 125 = 0
and factor the left side, you should have
(x + 25)(x - 5) = 0

Set each factor equal to 0 and solve. You'll get the same solutions.....
x = -25 or x = 5

Check....
(-25)^2 + 20(-25) = 125
625 - 500 = 125
125 = 125

5^2 + 20(5) = 125
25 + 100 = 125
125 = 125

Both solutions check in the original problem. If your solution was marked wrong, it is because YOUR method would not produce these solutions.