Using Sine.
Sine = Opposite / Hypotenuse
sin 60° = a / (6√3) But sin60° = √3/2
√3/2 = a/(6√3)
Cross multiply
2*a = 6√3 * √3
2a = 6 * √(3*3)
2a = 6*3
a = 6*3/2
a = 3*3 = 9
Option E.
Hope this helps.
Over which interval(s) is the function decreasing?
1. A, It goes past the 4, but the circle is not shaded because the answer cannot be 4
2. C. It goes below the 11 and is shaded because it can be equal to 11
3. D. It is less than 13 and cannot equal thirteen, hence the non shaded circle
4. B. I goes past the -2 and has the circle shaded because it can be equal to the -2
Answer:
B., D., E.
Step-by-step explanation:

This is choice B.
This is choice E.
This is choice D.