(cos55°+sin45°sin10°)/(sin55°-cos45°cos80°)＝?
cos55°+sin45°sin10°
=cos(10°+45°)+sin45sin10
=cos10cos45-sin45sin10+sin45sin10
=cos10cos45
sin55-cos45cos80
=sin(10+45)-cos45cos80
=sin10cos45+sin45cos10-cos45cos80
=sin45cos10
sin45=cos45
∴原式=1