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Use completely the square to solve for x in the equation (x+7)(x-9)=25
5 months ago
Q:
Use completely the square to solve for x in the equation (x+7)(x-9)=25
Accepted Solution
A:
You mean "completing the square," don't you? ;)
(x+7)(x-9)=25 can be expanded: x^2 - 9x + 7x - 63 + 25, which becomes
x^2 -2x = 38.
Let's now complete the square:
x^2 - 2x + (1)^2 - (1)^2 = 38, or x^2 - 2x + 1 = 39
Rewrite that as (x-1)^2 = 39
Take the sqrt of both sides: x-1 = plus or minus sqrt(39)
Write the roots: x = 1+sqrt(39) and x = 1 = sqrt(39) (answers)