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Question 1022567: If the square of an integer is decreased by 20 the result is equal to eight times the original number. Find all possible values of the number.
Answer by addingup(3677)   (Show Source):
You can put this solution on YOUR website! x^2-20 = 8x
Subtract 8x from both sides:
x^2-8x-20 = 0
Now we have trinomial we can factor using FOIL (First, Outer, Inner, Last).
The left hand side factors into a product with two terms:
(x-10)(x+2) = 0
Let's now divide this into two equations:
x-10 = 0 or x+2 = 0
x = 10 or x = -2
Only one of these makes our original equation true, that's the number we want. Let's try them one at the time:
10^2-20 = 8(10)
100-20 = 80 This is our number, discard the other.
Your answer is:
x = 10
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