View Full Version : Establishing identities
lorraine_09
Jul 27, 2009, 07:56 AM
establish this identity:
cosx + 1+sinx = 2 sec x
1+sinx cosx
establish this identity:
sec(squared)x - tan(squared)x + tan x = sin x + cos x
sec x
Thank you so much any help would be great!! :)
Unknown008
Jul 27, 2009, 08:52 AM
1.
\frac{cos(x)}{1+sin(x)} + \frac{1+sin(x)}{cos(x)} = 2 sec(x)
Make everything a single fraction:
\frac{cos^2(x)+(1+sin(x))^2}{(1+sin(x))(cos(x))}
Then simplify:
\frac{cos^2(x)+1+2sin(x)+sin^2(x)}{(1+sin(x))(cos( x))}
\frac{(cos^2(x)+sin^2(x))+1+2sin(x)}{(1+sin(x))(co s(x))}
\frac{1+1+2sin(x)}{(1+sin(x))(cos(x))}
\frac{2+2sin(x)}{(1+sin(x))(cos(x))}
\frac{2(1+1sin(x))}{(1+sin(x))(cos(x))}
\frac{2}{(cos(x))}
2sec(x)
Unknown008
Jul 27, 2009, 08:58 AM
2.
\frac{sec^2(x) - tan^2(x) + tan (x)}{sec(x)} = sin( x) + cos( x)
Use: tan^2(x) + 1 = sec^2(x)
\frac{(tan^2(x) +1) - tan^2(x) + tan (x)}{sec(x)}
\frac{tan^2(x) +1 - tan^2(x) + tan (x)}{sec(x)}
\frac{(tan^2(x) - tan^2(x))+1 + tan (x)}{sec(x)}
\frac{1 + tan (x)}{sec(x)}
Convert everything into cos and sin.
\frac{1 + \frac{sin(x)}{cos(x)}}{\frac{1}{cos(x)}}
\( 1 + \frac{sin(x)}{cos(x)}\) \times cos(x)
cos(x) + sin(x)
Hope all helped! :)
lorraine_09
Jul 27, 2009, 09:12 AM
Yes thank you but how do I make each side equal to the other like 1=1 for example?
Unknown008
Jul 27, 2009, 09:19 AM
in fact, I should have typed :
\frac{cos(x)}{1+sin(x)} + \frac{1+sin(x)}{cos(x)} = \frac{cos^2(x)+(1+sin(x))^2}{(1+sin(x))(cos(x))}
Then continue with the simplifying. You just have to show that they are equal at the end, putting for example 'shown' or 'proved' at the end.
lorraine_09
Jul 27, 2009, 09:22 AM
OK yes thank you very much again! Have a great day!
Unknown008
Jul 27, 2009, 09:26 AM
A 'rating' would be nice from you too! :)
lorraine_09
Jul 27, 2009, 09:45 AM
OK I'm new at this today actually so I'm sorry but I don't know how to rate you! Could you help me out!
Unknown008
Jul 27, 2009, 11:47 AM
Just click on the 'rate this answer button, and follow what you are asked! :)