asinθ+bcosθ=1
acosθ−bsinθ=sinθ⋅cosθ square and add
a2+b2=1+sin2θcos2θ
=1+cos2θ−cos4θ
Now we have to get only b in L. H. S.
Multiply the given equation by cosθandsinθ and subtracting , we get
b(cos2θ+sin2θ)=cosθ−cosθ⋅sin2θ
or b = cos3θ∴cosθ=b1/3
∴a2+b2=1+b2/3−b4/3