What is the volume of each cone

Which sum or difference identity would you use to verify that cos (180° - q) = -cos q? a.) sin (a -b) = sin a cos b – cos a sin b b.) cos (a -b) = cos a cos b – sin a sin b c.) cos (a -b) = cos a cosb + sin a sin b d.) sin (a + b) = sin a cos b + cos a sin b

The difference of three and the reciprocal of a number is equal to the quotient of 20 and the number. find the number.

Solve the inequaliy: (x^2+2)(x−2)^2(6−2x)> 0