LHS: =

(using

)
We know

so we can replace the sin²x in the LHS expression as follows

which is the RHS.
Answer:
1 and 2 and 4
Step-by-step explanation:
Answer: C, 420
Step-by-step explanation:
The first positive even numbers are from 2 to 40, so the sum is equal to the number of terms, times the number of terms plus one (20*21 = 420)
the sum is 420