How to simplify the expression: sin(4x)sin(3x)-cos(4x)cos(3x)

Question

goformit100 · Answer

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goformit100 · Answer

use compound angle formula for solving this particular answer.

zepdrix · Answer

Here is the Cosine Angle Sum Identity:
$$\Large \cos \alpha \cos \beta-\sin \alpha \sin \beta\quad=\quad \cos(\alpha + \beta)$$
Hmm could we maybe alter our expression a little bit to fit this form?

anonymous · Answer

@zepdrix  : oh...thnks, simplify is cos7x, right ?

kainui · Answer

Not quite, you need to look closer. @evahenny

anonymous · Answer

@Kainui : and then, what the answer for my problem ?

kainui · Answer

You tell me! Just write the problem you have and the identity right next to each other and compare them closely. You might notice something is slightly different.

anonymous · Answer

@Kainui  : oh..thnks

kainui · Answer

=D

anonymous · Answer

@Kainui you are very smart :)