Posted by **Julie** on Thursday, April 12, 2012 at 12:50pm.

find the coordinates of all points on the graph of f(x) = x + 2cos(x) in the interval [0, pie] at which the tangent line is horizontal.

- Calculus grade 12 -
**Reiny**, Thursday, April 12, 2012 at 1:16pm
f'(x) = 1 - 2sinx

= 0 for a horizontal slope

1-2sinx = 0

sinx = 1/2

x = π/6 or 5π/5

if x = π/6

y = π/6 + √3 = (π + 6√3)/6 ---> point (π/6 , (π+6√3)/6

if x = 5π/6

y = 5π/6 - √3 = (5π - 6√3)/6 ---> point (5π/6 , (5π-6√3)/6 )

- Calculus grade 12 -
**Julie**, Thursday, April 12, 2012 at 3:31pm
thank you reiny

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