13、Trigonometric FunctionsExample 2 Differentiate f(x)=secx/(1+tanx).Solution f(x)=(secx)(1+tanx)-secx(1+tanx)/(1+tanx)2=secxtanx(1+tanx)-secxsec2x/(1+tanx)2=secxtanx+secxtan2x-sec3x/(1+tanx)2=secx(tanx-1)/(1+tanx)221Example 3 Prove Proof First suppose that 0 x/2. Figur...