已知sin10°=k，则cos620°等于（　　）A. kB. -kC. ±kD. 1-k

网友回答

∵sin10°=k，
∴cos620°=cos（360°+260°）=cos260°=cos（180°+90°-10°）=-cos（90°-10°）=-sin10°=-k．
故选：B．======以下答案可供参考======
供参考答案1:
cos620°
=cos(360+260)
=cos260
=cos(360-100)
=cos(-100)
=cos100
=sin(90-100)
=sin(-10)
=-sin10
=-k供参考答案2:
cos620°
620÷90=6余80°
cos620°
=cos80°=sin10°=K供参考答案3:
k