Question

How do you simplify `4 sin 21 cos 21`?

Answer 1

`4sin(21^@)cos(21^@) = 2sin(42^@) ~~ 1.328`

Explanation:

Double angle formula for sine function:
`color(white)("XXX")2sin(theta)cos(theta) = sin(2theta)`

`4sin(21^@)(cos(21^@)) = 2(sin(2xx21^@)) = 2sin(42^@)`

Using a calculator:
`color(white)("XXX")2sin(42^@) = 1.328`