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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