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January 25, 2015

January 25, 2015

Posted by **mike** on Monday, April 6, 2009 at 3:46pm.

i'm not completely sure that this is right but i used the difference of two squares on it to get (sin(a)+cos(b))(sin(a)-cos(b)) then after that i am stuck. please help

- math -
**Reiny**, Monday, April 6, 2009 at 4:32pmIt will surprise you to see how easy this one is.

we know that sin^2 a + cos^2 a = 1

and sin^2 b + cos^2 b = 1

then

sin^2 a + cos^2 a = sin^2 b + cos^2 b

now let's "move" the terms cos^2 a and cos^2 b to get the needed equation

sin^2 a - cos^2 b = sin^2 b - cos^2 a

Done!

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