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View Full Version : Came up with a second personalized proof...(is it correct)

Miike012
May21-11, 09:12 PM
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Miike012
May21-11, 09:19 PM
proof of sin(90 + theta) = cos(theta)
HallsofIvy
May22-11, 06:12 AM
Well, I wouldn't say "by construction angle COD is also theta". Since OD is perpendicular to AE, the only thing that is true "by construction" is that angle ODE and ODA are right angles. Now, you can they show that COD is theta by using the fact that the two angles in a right triangle are complementary- but you should show that.
praharmitra
May22-11, 09:47 AM
Wait. Am I missing something here. Shouldn't COD be 45-(theta/2) ?

AOE is an isosceles triangle. The perpendicular is also the angle bisector, right? Or have I understoond something wrong here?
Miike012
May22-11, 11:05 AM
Sorry.. after I looked at it... segment OD is not perp to segment AE.. and it doesnt have to be. I came up with a diff steps which I edited in the picture that I attached..