Answer:
10β
Step-by-step explanation:
We can find this two ways, first by seeing in the step after it, cosines are canceled out. Since you already have 10β
on the next step, you can assume that (since only the cosines changed and the cosine next ot the blank was removed), the value is 10
β
.
You can also use double angle formulas from the previous step:
(sin(2β) = 2 sin(β) cos(β))and find that:
5 sin (2β) sin(β) = 5 * (2 sin(β) cos(β)) sin(β)) = (10 sin(β) sin(β)) cos(β) =
10β
cos(β)
But since cos(β) is already present, we can see that the answer is 10β