sinx+cosx=sin30°
√2(√2/2*sinx+√2/2*cosx)=sin30°
√2sin(45°+x)=sin30°{√2sin(45°+x)=sin30°=1/2}
错×sin(45°+x)=√2/2=sin45°或sin135°
sin(45°+x)=1/2
x=-15°sinx+cosx=sin30° 代入x=00+1=sin30° ?√2(√2/2*sinx+√2/2*cosx)=sin30°√2sin(x+45°)=1/2√2sin(x+45°)=1/(2√2)sin(x+45°)=√2/4