sinx=o in the interval given , the possible value is none.
cosx=0 .In the given interval , the possible value is x=/π/2
b) find the 2nd derivative -2(sinx)^2+2 (cosx)^2=2cos2x
when you equate it to 0, in the given interval , you get x=π/4. When taking values within the given interval on both the sides of π/4, like π/6 , and plug in 2 nd derivative you get positive value. Taking x=π/2 , you get negative. The point of inflection is π/4.The max is π/2 and the min is π/6