cosAcosB+sinAsinB=0
sinAcosB-cosAsinB的值
是A +1 B -1 C±1呢
给出充分判断,题我已经化简完,就差结果
cosAcosB+sinAsinB=0
sinAcosB-cosAsinB的值
是A +1 B -1 C±1呢
给出充分判断,题我已经化简完,就差结果
cosAcosB+sinAsinB=cos(A-B)=0
∵cos²(A-B)+sin²(A-B)=1
∴sin²(A-B)=1,sin(A-B)=±1
sinAcosB-cosAsinB=sin(A-B)=±1,选C