Related Rates!! help please! A and B are walking on straight paths that meet at right angles. A approaches at 2m/sec; B moves away from the intersection at 1m/sec. At what rate is the angle [tex]\vartheta[/tex] changing when A is 10m from the intersection and B is 20m from the intersection. Ans in degrees per second. attempted solving the question using tan ratio where: tan[tex]\vartheta[/tex] (t)= A/B= (10-2t)/(20+t) I know i have to take the derivative of this equation in order to get d[tex]\vartheta[/tex] /dt, but how?