Question

10. Evaluate cos 48$°$ cos 42$°$ - sin 48$°$ sin 42$°$.

Answer 1

Dear Student,

$$\begin{gathered} Wehave, \\ \cos 48°.\cos 42°-\sin 48°.\sin 42° \\ \cos \left(90°-42°\right).\cos 42°-\sin \left(90°-42°\right).\sin 42° \\ \sin 42°.\cos 42°-\cos 42°.\sin 42°=0 \end{gathered}$$
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