Posted by **Evelina** on Saturday, November 12, 2011 at 9:06am.

Please help me how to do this:

1) 1 + sina*cosa / (cosa + sina)^2 =

2) sina + cosa / 1- 2sin^2a =

- trig -
**Reiny**, Saturday, November 12, 2011 at 9:27am
Are you sure the first one isn't

( 1 + 2sina cosa)/(cosa + sina)^2 ?

because then it would be

= (sin^2a + cos^2a + 2sina cosa)/(cosa + sina)^2

= (sina + cosa)^2/(cosa + sina)^2

= 1

2nd:

(sina + cosa)/(1 - 2sin^2a)= (sina + cosa)/(sin^2a + cos^2a - 2sin^2a)

= sina+cosa)/( cos^2a - sin^2a)

= (sina + cosa)/( cosa - sina)(cosa+sina) )

= 1/(cosa - sina)

- trig -
**Evelina**, Saturday, November 12, 2011 at 9:37am
oh yes, I wrote the first one wrong.

THANK YOU

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