Use the special right angle triangle to find cos 90
Firstly, we will be 45, 45, and 90 triangles
Cosine = Ajacent / hypotenus
Secondly, we need to find the hypotenus
[tex]\begin{gathered} \text{Hypotenus}^2=x^2+x^2 \\ \text{Hypotenus}^2=2x^2 \\ \text{Hypotenus = }\sqrt[]{2}\text{ x }\sqrt[]{x^2} \\ \text{Hypotenus = x}\sqrt[]{2} \end{gathered}[/tex]Since , cosine = Adjacent / Hypotenus
[tex]\begin{gathered} Co\sin e\text{ = Adjacent / Hypotenus} \\ Co\sin e\text{ 90= }\frac{x}{x\sqrt[]{2}} \\ \text{Cos 90 = }\frac{1}{\sqrt[]{2}} \end{gathered}[/tex]
