第990题：口诀
sin75°=?\sin 75 \degree = ?sin75°=?
A. 6+24\dfrac{\sqrt{6}+\sqrt{2}}{4}4√6+√2
B. 5+24\dfrac{\sqrt{5}+\sqrt{2}}{4}4√5+√2
C. 6−24\dfrac{\sqrt{6}-\sqrt{2}}{4}4√6−√2
D.5−24 \dfrac{\sqrt{5}-\sqrt{2}}{4}4√5−√2
sin(α+β)=\sin(\alpha + \beta)=sin(α+β)= sinαcosβ+cosαsinβ\sin \alpha \cos \beta + \cos \alpha \sin \betasinαcosβ+cosαsinβ
口决：正余余正，符号相同.
