Please help me prove this trig identity (please include justification)

(sinA^4 - cosA^4) secA^2 =secA^2-2

appreciated

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- June 10th 2012, 11:31 AMdanny88Math Trig Identity
Please help me prove this trig identity (please include justification)

(sinA^4 - cosA^4) secA^2 =secA^2-2

appreciated - June 10th 2012, 11:56 AMReckonerRe: Math Trig Identity
- June 10th 2012, 12:18 PMdanny88Re: Math Trig Identity
I would really appreciate if you would show me step by step because I seem to be making an error in my steps.

- June 10th 2012, 12:20 PMReckonerRe: Math Trig Identity
- June 10th 2012, 12:24 PMdanny88Re: Math Trig Identity
(sin^2 A+cos^2 A)(sin^2A-cos^2A) * sec^2A

(1)*(sin^2A-cos^2A) * sec^2A

1*(sinA-cosA)^2 * sec^2A

1*(1-2sinAcosA)* sec^2A - June 10th 2012, 12:35 PMReckonerRe: Math Trig Identity
- June 10th 2012, 12:41 PMdanny88Re: Math Trig Identity
sin^2 A/ cos^2A =tan^2A?

then -cos^2A/cos^2A= -1 ? - June 10th 2012, 12:44 PMReckonerRe: Math Trig Identity
- June 10th 2012, 12:48 PMdanny88Re: Math Trig Identity
1= sec^2A-tan^2A

but how does that work out? - June 10th 2012, 12:51 PMReckonerRe: Math Trig Identity
- June 10th 2012, 12:55 PMdanny88Re: Math Trig Identity
thanks a lot of the help, I really appreciate it.