thank you, who ever does this, i really appreciate your help its a hard question, so could you set it out in easy steps. thanks again!
differentiate sec²y by chain rule x=sec²y let sec y = t so that dt/dy = secy.tany x= t² so dx/dt = 2t dx/dy = dx/dt x dt/dy = 2t.secy.tany = 2 sec²y.tany