Question

Simplify the expression sin^2x-1/cos(-x)

Answer 1

Use the Pythagorean identity $sin ^{2} x+cos ^{2} x=1$
to simplify the numerator.
$sin ^{2} x-1=-cos ^{2} x$
Now use that fact that
$cos(-x)=cos(x)$ to set up the equivalent fraction:
$\frac{sin ^{2}x-1 }{cos(-x)} = \frac{-cos ^{2}x }{cos(x)}$
Now reduce between the numerator and denominator to get -cos(x)