# A geometric proof for the “small angle approximation” for the sine, cosine and tangent

How can be deduced the so called "small angle approximations" for sine, cosine and tangent, namely

$\sin \theta \approx \theta$

$\tan\theta \approx \theta$

$\cos\theta \approx 1-\frac{\theta^2}{2}$

By means of any geometric construction? Of course, here $\theta$ is in radians. How to prove these approximations by means of geometry?