The double angle formula for the sine is

The right hand side is exactly your expression, where 
So, rewriting the expression from right to left, we have

Answer:
b = 1
Step-by-step explanation:
Given the equation is:
- 5b + 2b - (-b) + 7 = 5
We separate the terms of b and the constants. To do that we subtract 7 from both the sides. We get:
- 5b + 2b - (-b) + 7 - 7 = 5 - 7
⇒ - 5b + 2b - (-b) = - 2
Now, simplifying the terms with 'b'.
⇒ -5b + 2b + b = - 2
⇒ (-5 + 2 + 1)b = - 2
⇒ -2b = -2
Dividing both the sides by -2, we get:
b = 1 which is the required answer.
Options 1 does not represent a function
Answers:
2x - 6y = 8 -> x = 4 + 3y
-3x + 9y = 12 -> x = -4 + 3y