The answer is B) 1/4.
There are 2 outcomes in his tree that have all coins with the same side up: HHH and TTT. There are 8 total outcomes. This makes the probability 2/8 = 1/4.
Hi there!
To solve, we must use the following trig identity:
sin(u - v) = sin(u)cos(v) - sin(v)cos(u)
We can rewrite the left hand side of the equation as:

Split the fraction:

First fraction reduces to 1:

Simpify each with common arguments:

24
x
^2
+
54
x
+
21,
if you would like me to explain how to do it, I can in the comments.
Multiply straight across (neg times a neg = a positive)
=28/81