Question

Найдите значение выражения:
1)$frac{31cos67.}{sin23.}$
2)$frac{20( sin^{2}49.- cos^{2} 49.) }{cos98.}$

Answer 1

$frac{31*cos67 ^{0} }{sin23 ^{0} } = frac{31*cos( 90^{0}-23 ^{0} )}{sin 23^{0} } = frac{31*sin 23^{0} }{sin 23^{0} } =31$
$frac{20*( sin^{2} 49^{0} - cos^{2} 49^{0} )}{cos98 ^{0} } = frac{20*(-1)*(cos ^{2}49 ^{0} - sin^{2} 49^{0} )}{cos 98^{0} } = frac{-20*cos(2* 49^{2} )}{cos 98^{0} }=$
$= frac{-20*cos98 ^{0} }{cos98 ^{0} } =-20$