Answer:
-3.8
Step-by-step explanation:
u = 3.8
u × -1 = 3.8 × -1
-u = -3.8
Whole numbers are like 0,1,2,3,4,5...
the smallest one is 10
prime numbers
I do not accept 1 as a prime number, if you agree, go to AAAAAAAAA
if you do think it's a prime number, go to BBBBBBB
AAAAAAA
2,3,5,7
2+3+5+7=17
a+b=10+17=27
BBBBBBBBBBB
1,2,3,5,7
1+2+3+5+7=18
a+b=10+18=28
if you do not think a is a prime number, then the answer is 27
if you do think 1 is prime number then the answer is 28
This is one pathway to prove the identity.
Part 1

Part 2

Part 3

As the steps above show, the goal is to get both sides be the same identical expression. You should only work with one side to transform it into the other. In this case, the left side transforms while the right side stays fixed the entire time. The general rule is that you should convert the more complicated expression into a simpler form.
We use other previously established or proven trig identities to work through the steps. For example, I used the pythagorean identity
in the second to last step. I broke the steps into three parts to hopefully make it more manageable.