Q - in the solution

x(t) = q.exp-at . sin(Gt-d) describing the transients for a lightly damped oscillator, show that the local maxima and minima of q occur at roots of tan(Gt-d) = G/a.

Then by sketching the graph of tan [theta] deduce that these stationary valus occur at equal time intervals pi/G

i desperately need help with this! i havent a clue where to start!