Prove this trig identity

Using sin=y/2, cos=x/r, tan=y/x

prove the identity 1+tan^2=1/cos^2

Cant figure this one out.

Thanks in advance!

This is a version of 1+( tanB)^2=(sec B)^2

But you also need Pythagorean theorem, x^2 + y^2=r^2

using B for the angle:

1+ ( tanB)^2=

1+(y/x)^2

(x/x)^2+(y/x)^2

(x^2+y^2)/x^2

r^2/x^2

=1/(x^2/r^2)

=1/(x/r)^2

=1/(cosB)^2

Hoping this helps!