How can i use decimal models to subtract decimals? ?

What properties allow transformation to be used as a problem solving tool

How do you use the elimination method for this question? explain, because i really want to understand!

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