Question

tana=3 则1/sin2a+cos2a=?

Answer 1

原式=1/2sinacosa+cosa^2-sina^2=(sina^2+cosa^2)/j2cosasina+(cosa^2-sina^2)/(cosa^2+sina^2)=(tana^2+1)/2tana+(1-tana^2)/(1+tana^2)=10/6-8/10=13/15