What equation correctly uses the law of cosines to solve for the missing side length of triangle PQR

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

What would the rule be for the reflection of y=-3

Which equation is y = -6x2 + 3x + 2 rewritten in vertex form?