SOLUTION: Convert the equation y(x)= -2(x-k)^2 + 4 into the standard form. Assume k is a constant whose value you do not know. I keep ending up with an extra k that doesn't fit into the

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: Convert the equation y(x)= -2(x-k)^2 + 4 into the standard form. Assume k is a constant whose value you do not know. I keep ending up with an extra k that doesn't fit into the       Log On


   

Question 320392: Convert the equation y(x)= -2(x-k)^2 + 4 into the standard form. Assume k is a constant whose value you do not know.
I keep ending up with an extra k that doesn't fit into the standard equation:
y(x)= -2(x-k)^2 + 4
= -2(x-k)(x-k)+4
= -2(x^2 -xk -xk +k)+4
= -2(x^2-2xk +k)+4
= -2x^2 +4xk +k +4 not quite standard form!
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Your derivation is correct except you made a small mistake by not distributing correctly,
y%28x%29=+-2%28x%5E2-2xk+%2Bk%29%2B4
y%28x%29=+-2x%5E2+%2B4xk-2k+%2B4
y%28x%29=-2x%5E2%2B4kx%2B%284-2k%29
Comparing to the general equation
y%28x%29=ax%5E2%2Bbx%2Bc
a=-2
b=4k
c=4-2k
Since k is a constant, 4-2k is also just a constant.