Posted by **Shelley** on Tuesday, October 4, 2011 at 10:31pm.

For what values of x does the graph of f(x)=x+2sinx have a horizontal tangent?

- calculus -
**Reiny**, Tuesday, October 4, 2011 at 10:42pm
f'(x) = 1 + 2cosx

= 0 for a horizontal tangent , (slope=0)

2cosx = -1

cosx = -1/2

x must be in quadrants II or III

and I know that cos π/3 = +1/2

x = π-π/3 or x = π + π/3

x = 2π/3 or x = 4π/3 , for 0 ≤ x ≤ 2π

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