（1／sin10度）－根号3／cos10度
=1/sin10°-√3/cos10°
=(cos10°-√3sin10°)/(sin10°cos10°)
=2[(1/2)cos10°-(√3/2)sin10°]/(sin10°cos10°)
=4[(1/2)cos10°-(√3/2)sin10°]/(2sin10°cos10°)
=4(cos60°cos10°-sin60°sin10°)/sin20°
=4cos(60+10)°/sin20°
=4cos70°/sin20°
=4