SOLUTION: x minus the square root of -2x+21 = 9. What does x equal? Im not sure how to write the radical sign but -2x+21 is whats under the radical sign.

Question 146734: x minus the square root of -2x+21 = 9.
What does x equal?
Im not sure how to write the radical sign but -2x+21 is whats under the radical sign.

Answer by nabla(475) (Show Source): You can put this solution on YOUR website!
x - Sqrt[-2 x + 21] = 9
Sqrt[-2 x + 21] = x - 9
-2 x + 21 = x^2 - 18 x + 81
0 = x^2 - 16 x + 60
0 = (x-6)(x-10)
gives x=6 or x=10,
but x=6 makes 6 - Sqrt[9]=3 which is not= 9. We therefore exclude this solution.
Leaving x=10 as the solution.
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