1.$(sin\theta+cos\theta)^{2}$ =1+2sin$\theta$·cos$\theta$.
2.$(sin\theta-cos\theta)^{2}$ =1-2sin$\theta$·cos$\theta$.
3.$\frac{sin\alpha}{\sqrt{1-cos^{2}\alpha}}+\frac{\sqrt{1-sin^{2}\alpha}}{cos\alpha}= 2，\alpha∈(0，\frac{π}{2})$
4.$\frac{\sqrt{1-2sin\alpha·cos\alpha}}{sin\alpha-\sqrt{1-sin^{2}\alpha}} =1，\alpha∈（\frac{π}{4}，\frac{π}{2}）$