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(xy) 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