Question

Вычислите : -30/cos^2 87+cos^2 177

Answer 1

$-\dfrac{30}{\cos^287^\circ+\cos^2177^\circ}=-\dfrac{30}{\cos^287^\circ+\cos^2(90^\circ+87^\circ)}=\\ \\ \\ =-\dfrac{30}{\cos^287^\circ+\sin^287^\circ}=-\dfrac{30}{1}=-30$