Posted by khela on Thursday, October 28, 2010 at 6:12pm.
find the points to the curve
y=(cos x)/ (2 + sin x)
at which the tangent is horizontal...
can you explain how get the answer thoroughly and step by step...

math  Reiny, Thursday, October 28, 2010 at 6:44pm
using the quotient rule,
dydx = [(2+sinx)(sinx)  cosx(cosx)]/(2+sinx)^2
a horizontal tangent implies the slope is zero, that is, the derivative is zero.
(2+sinx)(sinx)  cosx(cosx) = 0
2sinx  sin^2x  cos^2x = 0
2sinx  (sin^2x + cos^2x) = 0
2sinx  1 = 0
sinx = 1/2
x = 7π/6 or x = 11π/6 ..... (210° or 330°)
sub 7π/6 and 11π/6 into the original equation to find the corresponding y values.
Those will give you the points in the domain 0 ≤ x ≤ 2π
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