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Posted by on Saturday, March 27, 2010 at 1:06pm.

the expression cos4x cos3x + sin4x sin3x is equivalent to
which one of the following is the answer:
1) sinx
2) sin7x
3) cosx
4) cos7x

  • math(advanced algebra&trigonometry) - , Saturday, March 27, 2010 at 3:33pm

    Look up the equation for cos(x-y) and it should be obvious what the answer is.

    Think of x as 4x and y as 3x.

  • math(advanced algebra&trigonometry) - , Sunday, March 28, 2010 at 11:47am

    it is cosx

  • math(advanced algebra&trigonometry) - , Monday, October 4, 2010 at 12:17am

    Seca=4x + 1/x than secb + tana what please tell me after 2days

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