Question

已知Sin（45度＋∝）=1/则sin2∝=

Answer 1

sin（45°+a）=sinacos45°+sin45°cosa=(√2/2)(sina+cosa)=1/4;

两边平方得：(1/2)(sin²a+cos²a+2sinacosa)=1/16;

1+sin2a=1/8;

sin2a=-7/8;