Question

cos $1^o$ cos $2^o$ cos $3^o$ ..... cos ${180}^o$ = ?

(a) -1 (b) 1 (c) 0 (d) $\frac{1}{2}$

Answer 1

cos $1^o$ cos $2^o$ cos $3^o$ ..... cos ${180}^o$

= cos $1^o$ cos $2^o$ cos $3^o$ .....cos ${90}^o$ .... cos ${180}^o$

=cos $1^o$ cos $2^o$ cos $3^o$ ..... $\times$ 0 $\times$ cos ${180}^o$

= 0

Hence, the correct choice is (c).