Use trig identities to verify this expression:
((1-tan^2(x))/(sec^2(x))=cos(2x).

Can someone pls ! pls answer all. no explanation needed..

The ratio of the measures of the three angles in a triangle is 2: 9: 4. find the measures of the angels

Type the correct answer in the box. consider the system of linear equations below. rewrite one of the two equations above in the form ax + by = c, where a, b, and c are constants, so that the sum of the new equation and the unchanged equation from the original system results in an equation in one variable.