Question

Find the value of: $\cos {38}^o\times \cos {52}^o-\sin {38}^o\times \sin {52}^o$

Answer 1

$\cos {38}^o\times \cos {52}^o-\sin {38}^o\times \sin {52}^o$

= $\sin (90-52{)}^o\times \sin (90-38{)}^o-\sin {38}^o\times \sin {52}^o$

= $\sin {38}^o\times \sin {52}^o-\sin {38}^o\times \sin {52}^o$

= $0$