# LHS = cos10cos20 + sin45cos145 + sin55cos245 #
# = 1/2 2cos10cos20 + 2sin45cos145 + 2sin55cos245 #
# = 1/2 Cos (+ 20 10) + cos (20-10) + sin (45 + 145) -sin (145-45) + sin (245 + 55) -sin (245-55) #
# = 1/2 cos30 + cos10cancel (+ sin190) -sin100 + sin300cancel (-sin190) #
# = 1/2 sin (90-30) + cos10-sin (90 + 10) + sin (360-60) #
# = 1/2 iptal (sin60) iptal (+ cos10) iptal (-cos10) iptal (-sin60) #
# = 1/2 * 0 = 0 =, RHS #
