Posted by Anonymous on Friday, June 22, 2012 at 8:24am.
Find the derivative of the function y defined implicitly in terms of x.
y = sqrt(xy + 9)
Please help! Thanks! :)

Calculus  Reiny, Friday, June 22, 2012 at 8:55am
Did you mean "with respect to x" ?
If so then I would square both sides
y^2 = xy + 9
2y dy/dx = x dy/dx + y
2y dy/dx  x dy/dx = y
dy/dx(2yx) = y
dy/dx = y/(2yx) such that √(xy9) ≥ 0
if you want that expression to be in terms of x only, (like you typed)
we have a mess ahead
we would have to solve
y^2  xy  9 = 0 for y in terms of x
y = (x ± √(x^2 +36) )/2
and sub that into dy/dx to get only x's
so I will wait for your clarification before I start that messy substitution.
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