SOLUTION: Find inverse of function f(x) = x^2 - 5x ?

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Question 1166430: Find inverse of function f(x) = x^2 - 5x ?
Found 2 solutions by harpazo1965, greenestamps:
Answer by harpazo1965(1) About Me  (Show Source):
You can put this solution on YOUR website!
f(x) = x^2 - 5x

Let y = f(x)

y = x^2 - 5x

x = y^2 - 5y

x = y(y - 5)

x/(y- 5) = y


Here, y cannot be isolated. This function does not have an inverse.

Answer by greenestamps(13206) About Me  (Show Source):
You can put this solution on YOUR website!


The solution by the other (newcomer) tutor is incorrect.

Note the given function graphs as a parabola. The function has an inverse; but the inverse will not be a function.

To find the inverse, switch the x and y and solve for the new y.

x+=+y%5E2-5y

To solve for y, you need to complete the square in y.

x+=+y%5E2-5y
x+=+%28y%5E2-5y%2B25%2F4%29-25%2F4
x+=+%28y-%285%2F2%29%29%5E2-25%2F4
%28y-%285%2F2%29%29%5E2+=+x%2B25%2F4
y-5%2F2+=+%28sqrt%28x%2B25%2F4%29%29 OR y-5%2F2+=+-%28sqrt%28x%2B25%2F4%29%29

y+=+%28sqrt%28x%2B25%2F4%29%29%2B5%2F2 OR y+=+-%28sqrt%28x%2B25%2F4%29%29%2B5%2F2