Suppose y varies directly as x and y=21 when x=3 find x when y=42

Find the value of the variable and the length of each secant segment.

What is best way to getting answer for my exam is

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