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there is something wrong in the expression!!

the tan-1 is inverse tan not minus 1

oh I see

sorry about that

sorry i was grabbing lunch

OK then. Do you see where I'm going, though?

yeah i understand. a^2 +b^2 = c ^2. what i don't understand is where the 2 comes int0 play

before the tangent

im sorry but that doesn't make any sense to me. my brain is peicing together what you're saying

piecing*

Does that image help explain it better?

hold on one second

You know tan(a) = x by definition

okay so cos(2a) got it. so you're just using tan to find the value's of the triangle?

Yes, from which you can work out cos (or sin, but you don't need both here)

ohhhhh okay. tan-1x = a ? so 2tan-1x = 2a right then cos(2a) is what i want?

Yes, indeed :D

ahh thanks let me work it out and ill reply with an answer

cos(2sqrt(1+x^2)/x) ?

my book says the answer is (1-x^2)/(1+x^2)

but idk how to get there

okay yes

Sorry the simplification/fraction look messy but hopefully the brackets make it clear

those are pythag identities ?

thats what i was missing. i didin't know i was supposed to be using those to get my answer.

no no i meant...

cos^2 - 1

that's part of cos^2 + sin^2 = 1 right?

you used that to get the answer?

okay thanks! off to take my test.

Have fun!

lol sure