If sinY1+cosY=1a, then prove that a21a2+1=cosY.
 
Proof:
 
sinY1+cosY=1a
 
 
\(a^2 =\)
 
\(a^2 + 1 =\)
 
\(a^2 - 1 =\)
 
LHS \(=\) a21a2+1
 
\(=\)
 
\(=\)
 
\(=\)
 
\(=\) cosY
 
\(=\) RHS
 
Hence, we proved.
Answer variants:
2cos2Y+2cosYsin2Y
1+cos2Y+2cosYsin2Y
2cos2Y+2cosY2+2cosY
a=1+cosYsinY
2+2cosYsin2Y
2cos2Y+2cosYsin2Y2+2cosYsin2Y
2cosY(cosY+1)2(1+cosY)