tanxtan(x+100°)=tan(x+50°)tan(x−50°)
cos(x+100°)sinxsin(x+100°)cosx=cos(x+50°)cos(x−50°)sin(x+50°)sin(x−50°)
Applying Componendo & Dividendo:
sin100°sin(2x+100°)=−cos2xcos100°
2sin(2x+100°)cos2x+sin200°=0
sin(4x+100°)+sin100°+sin200°=0
sin(4x+100°)=−2sin150°cos50°
sin(4x+100°)=−cos50°=sin(−40°)
∴4x+100°=nπ+(−1)n(−40°)
x=4nπ+(−1)n+1(40°)−100°
∴x=30°,55°,120°,145° in (0,π)
∴ Number of solutions =4