Question

what's 9+10?

Answer 1

stop...

Answer 2

ok

Answer 3

i am so sorry my brother was on

Answer 4

@xMissAlyCatx

Answer 5

\(\large\color{black}{ \displaystyle {\rm Cos}(a-b)= {\rm Cos}(a) {\rm Cos}(b)+ {\rm Sin}(a) {\rm Sin}(b) }\)
(this rule can be also proven - geometrically)

Therefore:
\(\large\color{black}{ \displaystyle {\rm Cos}(\theta-\theta)= {\rm Cos}\theta{~}{\rm Cos}\theta+ {\rm Sin}\theta{~}{\rm Sin}\theta }\)
\(\large\color{black}{ \displaystyle {\rm Cos}(0)= {\rm Cos}^2\theta+ {\rm Sin}^2\theta }\)
\(\large\color{blue}{ \displaystyle1= {\rm Cos}^2\theta+ {\rm Sin}^2\theta }\)