Q. When input is a triangular wave.

When the input fed to differentiating circuit is a triangular wave, the output will be a rectangular wave.

During the period OA of the input wave its amplitude changes at a constant rate and therefore the differentiated wave has a constant value for each constant value for each constant rate of change .During the period AB of the input wave, the  change is less abrupt so that the output will be a very narrow pulse of rectangular form. Thus when a rectangular wave is fed to a differentiating circuit , the output  consists of a succession of rectangular waves of equal or unequal duration depending upon the shape of the input wave. When input is a sine wave.- A sine wave input becomes a cosine wave and a cosine wave input becomes an inverted sine wave at the output .