Posted by **Rony** 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) -
**drwls**, 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.

http://www.csgnetwork.com/trigtriformulatables.html

- math(advanced algebra&trigonometry) -
**Rony**, Sunday, March 28, 2010 at 11:47am
it is cosx

thanks

- math(advanced algebra&trigonometry) -
**Dewesh kumar**, Monday, October 4, 2010 at 12:17am
Seca=4x + 1/x than secb + tana what please tell me after 2days

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