show that the curves r=asin(è) and r=acos(è) intersect at right angles.

can you show that the derivatives for each are the negative reciprocal of each other? That is the key.

i need more info..i know how to find the derivative...but how will that prove my question. Do I need to graph it after i find the derivatives?

The definition of perpendicular lines is that their slope is the negative reciprocal. The deravative is the slope.

You will need to determine the point of intersection, then evaluate the derivatives at that point. If one is the negative reciprocal of the other, then by definition, they are perpendicular.