Prove that: sinA+sinB+sinC=(4cosA÷2)(cosB÷2)(co sC÷2)​

How do i do this? i don’t understand

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

What is the solution of log2  (3x  -  7)  =  3? 4 5