Question

Cos and sin problems

Answer 1

\[0 < \theta < \frac{ \pi }{ 2 } \] and \[\cos \theta = \frac{ 2 }{ 5 }\]
Find sin theta

Answer 2

\[\cos(x)=\frac{2}{5}\]\[\cos^2(x)=\frac{4}{25}\]\[1-\cos^2(x)=1-\frac{4}{25}\]\[\sin^2(x)=\frac{21}{25}\]\[\sin(x)=\pm\frac{\sqrt{21}}{5}\]
For 0<x<pi/2, this gives the positive value: \(\frac{\sqrt{21}}{5}\)

Answer 3

Oh I forgot about that formula, I understand it, thanks!

Answer 4

No problem!