1.Biến đổi thành tích các biểu thức sau C = cos^2 (3a) + cos^2 (2a) - sin^2 a

I've never been good at math he told he loves but he keeps cheating on me, so it ain't adding up sis

What is the missing step in this proof ?

Aschool allots ? 1500 to spend on a trip to the theatre. theatre tickets have a regular cost of ? 55 each and are on offer for 1 5 off. a train ticket for the day will cost ? 12 each. if 2 teachers and the maximum number of students attend, how much money will the school have left over?