# why value of Trigonometric ratios of angle and its reference angle are same?

I'm learning Trigonometry right now with myself and at current about how to find trigonometry ratios of angles greater than $90^\circ$. I came to know that for finding trigonometric ratio of these angles we can use reference angle because they both have the same absolute numeric value. Can anybody tell me why they both have same trigonometric ratio. Is there any graphical or or any kind of proof to show this.

The tangent or the secant of $90^\circ$ is $\infty$, and this $\infty$ is neither $+\infty$ nor $-\infty$ but rather a single $\infty$ that is approached by going in either the positive or the negative direction along the line.
• Do you mean you can't see the images, or that you don't understand them? Or something else? $\qquad$ – Michael Hardy Jan 27 '16 at 19:29