是根号(1+sin100°)-根号(1-sin100°)吧?
根号(1+sin100°)-根号(1-sin100°)
=根号[ sin^2 (50°)+cos^2 (50°)+2sin50°cos50° ]-根号[ sin^2 (50°)+cos^2 (50°)-2sin50°cos50° ]
=sin50°+cos50°-(sin50°-cos50°)
=2cos50°