All you need is the double angle identity:

So we have

Apply the identity again to the squared term:

Dominic weighs 120.
I started laughing as soon as I saw this question...
It honestly made my day:)
Answer:
19+19= x
So x, is 38. Just add 19 and 19
Ik this is late, but people who are looking for the answer can see this.
Answer:
an =1/3*6^n-1
Step-by-step explanation:
You should plug in 2 for n in each equation, which, the correct one should give you 2. Then, to make sure, you plug in 3 in the equations that gave you 2.
Example:
an = 1/3 * 6 ^n-1
Plug in 2.
an = 1/3 * 6 ^2-1
an = 1/3 * 6 ^1
1/3 * 6 = 2
Step 2.
an = 1/3 * 6 ^3-1
an = 1/3 * 6 ^2
1/3 * 36 = 12
Hope this helps.