Re: Trigonometric identities

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Posted by Louis Feng on October 20, 1998 at 23:57:34:

In Reply to: Trigonometric identities posted by Janos Koplyay on October 12, 1998 at 17:23:42:

Hi Janos,

There are ways to do that, One way is write sin 5x as sin(3x+2x), cos 5x as cos(3x+2x), then use the Sum and Difference formulas to expand them. After that we can use Double & Triple Angle formulas to simplify the terms.

This is just an idea, Edward have other ways to do it and as well as the sin(n)x formulas. I will post it soon.

Hope they will help.

Best regards,

Louis

: Is there a method to find an identity formula forcos(5x), or cos(nx) where n is greater than 2?
: I am thinking of something like the identity for cos(2x)
: Thanks!

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Comments: : Hi Janos, : There are ways to do that, One way is write sin 5x as sin(3x+2x), cos 5x as cos(3x+2x), then use the <a href="http://hyperion.advanced.org/17119/je/memorize/s_d.html">Sum and Difference formulas</a> to expand them. After that we can use <a href="http://hyperion.advanced.org/17119/je/memorize/d_a.html">Double & Triple Angle formulas to simplify the terms</a>. : This is just an idea, Edward have other ways to do it and as well as the sin(n)x formulas. I will post it soon. : Hope they will help. : Best regards, : Louis : : Is there a method to find an identity formula forcos(5x), or cos(nx) where n is greater than 2? : : I am thinking of something like the identity for cos(2x) : : Thanks! : : Is there a method to find an identity formula forcos(5x), or cos(nx) where n is greater than 2? : : I am thinking of something like the identity for cos(2x) : : Thanks!

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