Question

Help me?

Answer 1

@jim_thompson5910 @Directrix @jdoe0001 @dan815 @e.mccormick @Kainui @TheSmartOne @Whitemonsterbunny17 @Nnesha @bibby @tHe_FiZiCx99 @camerondoherty

Answer 2

@jagr2713

Answer 3

Click the attachment

Answer 4

@hhelpplzzzz

Answer 5

@bohotness

Answer 6

srry i dont know

Answer 7

sorry i forgot

Answer 8

d or c

Answer 9

@bohotness how?

Answer 10

-_-

Answer 11

\(\large \begin{align} \color{black}{
\normalsize \color{blue}{\text{use identity} \cos(\theta)=\cos (90-\theta)} \hspace{.33em}\\~\\
\cos^2 2^{\circ}+\cos^2 4^{\circ}+\cos^2 6^{\circ}+\cdot \cdot \cdot \cdot \cdot+
\cos^2 90^{\circ} \hspace{.33em}\\~\\
=\sin^2 88^{\circ}+\sin^2 86^{\circ}+\sin^2 84^{\circ}
\hspace{.33em}\\~\\ +\cdot \cdot \cdot \cdot \cdot+\sin^2 2^{\circ}+\sin^2 0^{\circ}-------\color{red}{(1)} \hspace{.33em}\\~\\
\normalsize \color{blue}{\text{use identity} \cos^2 \theta=1-\sin^2 \theta} \hspace{.33em}\\~\\
\cos^2 2^{\circ}+\cos^2 4^{\circ}+\cos^2 6^{\circ}+ \hspace{.33em}\\~\\
\cdot \cdot \cdot \cdot \cdot+\cos^2 90^{\circ} \hspace{.33em}\\~\\
=45-(\sin^2 2^{\circ}+\sin^2 4^{\circ}+\sin^2 6^{\circ}+ \hspace{.33em}\\~\\
\cdot \cdot \cdot \cdot \cdot+\sin^2 90^{\circ})-------\color{red}{(2)} \hspace{.33em}\\~\\
\normalsize \color{blue}{\text{add 1 and 2}} \hspace{.33em}\\~\\
2(\cos^2 2^{\circ}+\cos^2 4^{\circ}+\cos^2 6^{\circ}+\cdot \cdot \cdot \cdot \cdot+\cos^2 90^{\circ}) \hspace{.33em}\\~\\
=\sin^2 88^{\circ}+\sin^2 86^{\circ}+\sin^2 84^{\circ}+\cdot \cdot \cdot \cdot +\sin^2 2^{\circ}+\sin^2 0^{\circ}+\hspace{.33em}\\~\\
45-(\sin^2 2^{\circ}+\sin^2 4^{\circ}+\sin^2 6^{\circ}+\cdot \cdot \cdot \cdot \cdot+\sin^2 90^{\circ} \hspace{.33em}\\~\\
=45-\sin^2 90^{\circ} \hspace{.33em}\\~\\
2(\cos^2 2^{\circ}+\cos^2 4^{\circ}+\cos^2 6^{\circ}+\cdot \cdot \cdot \cdot \cdot+\cos^2 90^{\circ})=44 \hspace{.33em}\\~\\
so~~\hspace{.33em}\\~\\
(\cos^2 2^{\circ}+\cos^2 4^{\circ}+\cos^2 6^{\circ}+\cdot \cdot \cdot \cdot \cdot+\cos^2 90^{\circ})=22 \hspace{.33em}\\~\\

}\end{align}\)