Question

(cos66cos42+cos24cos48)/(sin^2 12-cos^2 12)

Answer 1

(cos66cos42+cos24cos48)/(sin^2 12-cos^2 12)

(cos66cos42+cos24cos48)/(sin144-cos144) ≈ -0,0941943

Answer 2

$frac{cos66cdot cos42+cos24cdot cos48}{sin^212-cos^212}=frac{sin24cdot cos42+cos24cdot sin42}{-cos24}=-frac{sin(24+42)}{cos24}=\\=frac{sin66}{cos24}=-frac{cos24}{cos24}=-1\\\P.S.; ; cos66=cos(90-24)=sin24\\.; ; ; ; quad cos48=cos(90-42)=sin42$