Help!!

[Confused312]

I can't figure this out!

( 3 sin x + cos x) ( sin x + 3 cos x) - 13 cos x sin x
__________________________________________ = 3

cos x ( sec x - sin x )



I need to prove it and Im stuck! Please help!

 

[stapel]

I would start by multiplying out and simplifying the numerator; it simplifies a lot.

Factor the "3" out front.

Then convert the denominator to all sines and cosines, and multiply the cosine through the parenthetical part. This will simplify in a manner which will allow an immediate cancellation with the numerator, leaving you with the required value.

Eliz.

 

[Confused312]

i get this far and get stuck?


3 ( sin^2 x + cos ^2 x + 3sin x cos x - 4 cos x sin x )
____________________________________________ = 4

cos x ( cos ^2 x / sin x )


Where do I continute to from here?

 

[stapel]

How did the "3" on the right-hand side become a "4"?

You might want to check your multiplication in the numerator. Also, the subtraction in the denominator should not have turned into multiplication. Even after you multiply the cosine through the parentheses, you should still have a subtraction statement.

Eliz.