Answer:
π/4, or 3π/4
Step-by-step explanation:
dy/dx = cos(x)*cos(x)+sin(x)*[-sin(x)]=(cosx)^2-(sinx)^2=[1-(sinx)^2]-(sinx)^2 = 1-2(sinx)^2
Tangent line is horizontal, so dy/dx = 0
1-2(sinx)^2 = 0
(sinx)^2 = 1/2
sinx = [tex]\frac{1}{\sqrt{2}}, -\frac{1}{\sqrt{2}}[/tex]
Between 0 and pi, sinx >0
so sinx = [tex]\frac{1}{\sqrt{2}}[/tex]
x = π/4, or 3π/4
