Posted by **Anonymous** on Monday, March 3, 2008 at 4:49pm.

How do I do these problems?

Verify the identity.

a= alpha, b=beta, t= theta

1. (1 + sin a) (1 - sin a)= cos^2a

2. cos^2b - sin^2b = 2cos^2b - 1

3. sin^2a - sin^4a = cos^2a - cos^4a

4. (csc^2 t / cot t) = csc t sec t

5. (cot^2 t / csc t) = csc t = sin t

- verifying trigonometric identities -
**^quen^**, Tuesday, March 4, 2008 at 8:46pm
Learn your identites well in order to prove these.

1. (1+sina) (1-sina)

= 1-sina+sina-sin^2a

= 1-sin^2a

= cos^2a (according to identity)

2. cos^2b-sin^2b

you know that sin^2b = 1-cos^2b, so:

cos^2b-(1-cos^2b)

=cos^2b-1+cos^2b

=2cos^2b-1

3. sin^2a - sin^4a=

= sin^2a- (sin^2a)(sin^2a)

=(1-cos^2a)-(1-cos^2a)(1-cos^2a)

=1-cos^2a- (1-2cos^2a+cos^4a)

=1-cos^2a-1+2cos^2a-cos^4a

=cos^2a-cos^4a

I hope you can do the rest by yourself ;)

- verifying trigonometric identities -
**Anonymous**, Saturday, December 13, 2008 at 6:46pm
1-sin^2B

------------- = csc^2B-sec^2B

sin^2Bcos^2B

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