2tan13°/(1+tan(13°)tan(13°)

问题描述:

2tan13°/(1+tan(13°)tan(13°)

2tan13°/(1+tan(13°)tan(13°)=2sin13/cos13 /(1+(sin13/cos13)^2)= 2sin13/cos13 /((cos^2(13)+sin^2(13))/cos^2(13))= 2sin13/cos13/(1/cos^2(13))= 2sin13cos13=sin26^2表示平方