Posted by George on Friday, November 7, 2008 at 12:38am.
(a) Find dy/dx given that x^2+y^24x+7y=15.
(b) Under what conditions on x and/or y is the tangent line to this curve horizontal? Vertical?
For part A, I simplifid it to
(2x+4/2y+7)
For part B,I am confused on what to do?

Calculus  asia, Friday, November 7, 2008 at 4:21am
2x+2y.y'4+7y'=0
y'(2y+7)=(42x)
y'=(42x)/(2y+7) as you found:)

Calculus  drwls, Friday, November 7, 2008 at 5:59am
Assuming the y' formula is correct, the tangent is zero when y' = 0 (x = 2) and vertical when the denominator of y' is zero (y = 7/2). The corresponding y and x values can be solve for using the original equation.
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