Hey! So your question is saying that FIRST you would multiply by 20 and after that subtract by 15. so 20h first and then followed by -15 Your answer is A!
It wouldn't be in parenthesis because it said multiply the hours by 20, THEN subtract. Hope this helps!!
Right side of the equation: cos ( A - B ) - cos ( A + B ) = = cos A cos B + sin A sin B - ( cos A cos B - sin A sin B ) = = cos A cos B + sin A sin B - cos A cos B + sin A sin B = = 2 sin A sin B - left side of the equation ( correct )
