Double angle identity for cosine:

By the Pythagorean theorem, if

, it follows that

:

where we take the positive root because

, and

is non-negative throughout this domain.
So we have
Answer:
Well one do the square root of 16
Answer:
Step-by-step explanation:
by theorem :
f continu in [1 , 2]
f(1)×f(2) < 0 because : f(1) = -1 and f(2) = 15
so the equation f(x)=0 has at least one real root between x=1 and x=2
so :
2x-9 =6
2x= 15
x= 7.5
I think thats the answer.
X = 180 - 60 - 80
x = 40
hope it helps