Show that the tangent to P: y= ax^2+bx+c with gradient m has y intercept c-(m-b)^2/4a. thank you.
The procedure is simple, but there's a LOT of algebra!
I was lucky to get the answer on the first try . . .
Show that the tangent to: . with gradient
. . has y-intercept: .
The derivative of: .  .is: .
If the gradient is
Substitute into : .
The tangent has point . and slope
Its equation is: .