If cos2x+2cosx=1 then sin^2x (2-cos^2x)=a. 1b.-1C.-root 5D. Root 5

Answer is a) 1, firstly convert cos2x into cosx and given equation is as follows cos^2x + cosx = 1, nowfor finding value of the equation convert sin into cos and it is like this (1-cos^2 x) (2-cos^2 x) and further put the value of cos^2 x from the equation and after putting value it will came out as (cosx) (1+cosx) and its value is 1