What could be the minimum and maximum value of angle in a triangle? Sum of angles of a triangle is 180 degress. So while studying trigonometric ratios , I got surprised at cos0 and cos 180 values. Although cosine is ratio of adjecent and hypotenuse ,in case of cos0 with value 1 or cos180 with value 0,  i doubt that how can it be called as triangle where one angle is 0 or 180 degree?
It would be just be just a straight line rather than called as triangle,isn't it? Also I want to know what could be the minimum and maxmimum value of angle in the triangle ?

In a sense, there are two different notions of trigonometric functions — although they do agree with each other on their common domain, so to speak.
One concept is that of trigonometric functions of an acute angle in a right triangle. This definition ONLY makes sense for angles $0^{\circ}<\theta<90^{\circ}$, or $0<\theta<\frac{\pi}{2}$ in radians. There's no smallest or largest possible value of $\theta$ here (for example, $\theta$ can be an arbitrarily small positive number). But from this point of view, expressions like "$\cos(0^{\circ})$" or "$\cos(180^{\circ})$" certainly do NOT make any sense, because there are no such right triangles.
But then there's a much more general concept of trigonometric functions as functions defined for all real numbers. Geometrically, one possible way to introduce them is via the unit circle. With this definition, statements such as "$\cos(0^{\circ})=1$" or "$\cos(180^{\circ})=-1$" make perfect sense. And by the way, note that for angles lying within the first quadrant this definition coincides with the right triangle definition.
So the answer depends on the context. There are certainly no triangles with angles of $0^{\circ}$ or $180^{\circ}$. Whether that invalidates trig functions of such angles or not… see above.
