

Given,
tan θ = a/b ,
Now, (a sin θ + b cos θ)/(a sin θ - b cos θ)
= (a sin θ/cos θ + b cos θ/cos θ)/(a sin θ/cos θ - b cos θ/cos θ) {divide cos θ in numerator and denominator}
= (a tan θ + b)/(a tan θ - b)
= {a* a/b + b)/(a* a/b - b)
= {a2 /b + b)/(a2 /b - b)
= {(a2 + b2 )/b}/{(a2 - b2 )/b}
= (a2 + b2 )/(a2 - b2 )
