# identity problem

• November 1st 2009, 03:34 PM
yaykittyeee
identity problem
i'm having trouble on this one.

$sec^3A-cos^3A/secA-cosA=2+cos^2A+tan^2A$

i expand the numerator and eliminate the (secA-cosA) and i get..

$sec^2A+secAcosA+cos^2A=2+cos^2A+tan^2A$

and then i make secAcosA= to 1 but then i get stuck, could someone help me with this please?
• November 1st 2009, 04:00 PM
umgambit
Well,
sec²A+cosAsecA+cos²A=1/cos²+1+cos²A=(cos²+sin²)/cos²+1+cos²A=1+sin²/cos²+1+cos²A=2+tan²A+cos²A.