inverse for a polynomial? 2x^2-7+4x?

Question

if you can help me with a counter example feel free,

i think u have to complete the square first

Answer 1

I've just answered this on your first posting. Didn't see it until it had been there a while and then took a fair while giving you a detailed answer. Have a look now.

PS I just looked at Greg's solution, and yes, completing the square seems a nicer way of doing it than using the formula (as I suggested). However, notice that this solution isn't a function because of the +-. Same if you use the formula. You must restrict the value of x, say x >= (-1), and then just use the + in solving the quadratic. Also Greg made an error in completing the square: It should be
2(x^2 + 2x + 1) -7-2

PPS He also made an error in the "dividing by 2" step. Can you correct it?

Answer 2

y=2x^2+4x-7
y=2(x^2+2x)-7
y=2(x^2+2x+4)-7-8
y=2(x+2)^2-15
to find inverse, switch variables and solve for y
x=2(y+2)^2-15
(x/2)+15=(y+2)^2
y+2=+-Sqrt[(x/2)+15]
y=-2+-Sqrt[(x/2)+15]

yeah, Hy is right, sorry about that