Prove that tan(A)+tan(B)+tan(C)=tan(A)tan(B)tan(C)\tan(A) + \tan(B) + \tan(C) = \tan(A)\tan(B)\tan(C)tan(A)+tan(B)+tan(C)=tan(A)tan(B)tan(C) for any triangle ABCABCABC.
True; but only when none of the angles is obtuse
True; this identity holds for all triangles
False; the sum should be negative for obtuse triangles
False; this only holds for right triangles