prove thatcos40cos80cos160= - 1/8 Share with your friends Share 0 Anuradha Sharma answered this Given , cos 40.cos 80.cos 160=-18Taking LHS,cos 40.cos 80.cos 160=2 sin40.cos 40.cos 80.cos 1602 sin40=2 sin40.cos 40.cos 80.cos 1602 sin40= sin2×40.cos 80.cos 1602 sin40 [sin2A= 2sinAcosA]=sin80.cos 80.cos 1602 sin40 =2sin80.cos80.cos1602×2sin40=sin2×80.cos1602×2sin40 [2sinAcosA= sin2A]=sin160.cos1602×2sin40=2sin160.cos1602×2×2sin40=sin3208sin40Now we know that, sin320 = sin360-40=-sin40 putting this we get, sin3208sin40=-sin408sin40=-18 Hence proved. 0 View Full Answer
