Solving,
⇒(cos θ - sin θ)(cos θ + sin θ)[Dividing numerator and denominator by cos θ]⇒cos θ(cos θ - sin θ)cos θ(cos θ + sin θ)⇒cos θcos θ−cos θsin θcos θcos θ+cos θsin θ⇒1−tan θ1+tan θ[As tan θ=cos θsin θ]Substituting values we get⇒1−1251+125⇒1212−51212+5⇒1271217⇒717=273.
Hence, (cos θ - sin θ)(cos θ + sin θ)=273.