In a non-right triangle ABCABCABC, given cosAa=cosBb\frac{\cos A}{a} = \frac{\cos B}{b}acosA=bcosB, which of the following must be true?
The triangle is equilateral.
a2+b2=c2a^2 + b^2 = c^2a2+b2=c2
The triangle is right-angled at CCC.
The triangle is isosceles with a=ba = ba=b.