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Prove that: tan 8x – tan6x – tan 2x = tan 8x tan 6x tan 2x

Answer»

We have 8x = 6x + 2x 

⇒ tan 8x = tan(6x + 2x) 

We know that tan(A + B) = \(\frac{tanA+tanB}{1-tanAtanB}\)

⇒ tan 8x = \(\frac{tan\,6x+tan\,2x}{1-tan\,6x\,tan\,2x}\)

⇒ tan8x (1 – tan6x tan2x) = tan6x + tan2x 

⇒ tan8x – tan8x tan 6x tan2x = tan6x + tan2x 

∴ tan8x – tan6x – tan2x = tan8x tan6x tan2x 

Hence, proved.



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