Question

(7cos(7p/2 -a))/5sin(3p+a)

Answer 1

В числителе:
$7cos( frac{7 pi }{2}- alpha )=7cos( 2 pi +( pi +( frac{ pi }{2} - alpha )))=7cos( pi +( frac{ pi }{2} - alpha ))= \ =-7cos( frac{ pi }{2}- alpha )=-7sin alpha ;$
В знаменателе:
$5sin(3 pi + alpha )=5sin(2 pi +( pi + alpha ))=5sin( pi + alpha )=-5sin alpha;$
$frac{-7sin alpha }{-5sin alpha } = frac{7}{5}=1,4$