Question

1) 42√6*cos п/6*cos 3п/4

Answer 1

$42 sqrt{6} *cos frac{ pi }{6} *cos frac{3 pi }{4} =42 sqrt{6} * frac{ sqrt{3} }{2} *cos( pi - frac{ pi }{4}) =$$=42 sqrt{6} * frac{ sqrt{3} }{2} *(-cos frac{ pi }{4}) =-42 sqrt{6} * frac{ sqrt{3} }{2} * frac{ sqrt{2} }{2} =-63$