


Examples
Last updated at Dec. 16, 2024 by Teachoo
Transcript
Example 17 Prove that sin〖5x − 〖2sin 3x +〗sinx 〗/𝑐𝑜𝑠〖5x − 𝑐𝑜𝑠x 〗 = tan x Solving L.H.S. sin〖5x + 〖sin x − 〗2sin3x 〗/𝑐𝑜𝑠〖5x − 𝑐𝑜𝑠x 〗 = 〖(𝐬𝐢𝐧〗〖𝟓𝐱 + 〖𝐬𝐢𝐧 𝐱) − 〗〖𝟐 𝐬𝐢𝐧〗𝟑𝐱 〗/𝒄𝒐𝒔〖𝟓𝐱 − 𝒄𝒐𝒔𝐱 〗 Solving numerator and denominator separately sin 5x + sin x = 2 sin ((𝟓𝒙 + 𝒙)/𝟐) cos ((𝟓𝒙 − 𝒙)/𝟐) = 2 sin (6𝑥/2) cos (4𝑥/2) = 2 sin 3x cos 2x cos 5x – cos x = – 2 sin ((𝟓𝒙 + 𝒙)/𝟐) sin((𝟓𝒙 − 𝒙)/𝟐) = – 2 sin (6𝑥/2) sin (4𝑥/2) = – 2 sin 3x sin 2x Solving L.H.S 𝐬𝐢𝐧〖𝟓𝐱 + 〖𝐬𝐢𝐧 𝐱 − 〗2sin3x 〗/𝒄𝒐𝒔〖𝟓𝐱 − 𝒄𝒐𝒔𝐱 〗 Putting values = (𝟐 𝒔𝒊𝒏𝟑𝒙 𝐜𝐨𝐬𝟐𝒙 − 𝟐 𝐬𝐢𝐧𝟑𝒙)/(−𝟐 𝐬𝐢𝐧〖𝟑𝒙 𝒔𝒊𝒏𝟐𝒙 〗 ) = (2 sin3𝑥 (cos〖2𝑥 − 1)〗)/(−2 sin〖3𝑥 sin2𝑥 〗 ) = ( (cos〖2𝑥 − 1)〗)/(−sin2𝑥 ) = ( −(cos〖2𝑥 −1) 〗)/sin2𝑥 = (〖1 − 𝐜𝐨𝐬〗𝟐𝒙 )/𝒔𝒊𝒏𝟐𝒙 = (1 − (𝟏 − 𝟐 𝐬𝐢𝐧𝟐𝒙 ) )/(𝟐 𝒄𝒐𝒔𝒙 𝒔𝒊𝒏𝒙 ) = (1 − 1 + 2 sin2𝑥)/(2 cos〖𝑥 〗 sin𝑥 ) = (0 + 2 sin2𝑥)/(2 cos〖𝑥 〗 sin𝑥 ) = (𝟐 𝐬𝐢𝐧𝟐𝒙)/(𝟐 𝒄𝒐𝒔〖𝒙 〗 𝒔𝒊𝒏𝒙 ) = sin〖𝑥 〗/cos〖𝑥 〗 = tan x = R.H.S. Hence L.H.S. = R.H.S. Hence proved