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Can't find a way to solve(trig eqn)

Sin2A -1 = Cos2A
Well im stuck
Sin2A - 1 = 1 -2 Sin^2 A
Turning it into a quadratic won't work here since Sin2A = f(2x) .
Please advice
Use sin 2A = 2sinAcosA

You'll have a quadratic in sin A.
Original post by Bilbao
Sin2A -1 = Cos2A
Well im stuck
Sin2A - 1 = 1 -2 Sin^2 A
Turning it into a quadratic won't work here since Sin2A = f(2x) .
Please advice


sin⁡(2A)−cos⁡(2A)=1\sin(2A) - \cos (2A) = 1 which is 2sin⁡Acos⁡A−cos⁡2A+sin⁡2A=cos⁡2A+sin⁡2A2\sin A \cos A - \cos^2 A + \sin^2 A = \cos^2 A + \sin^2 A

This then reduces nicely.
Reply 3
Avatar for Bilbao
Bilbao
OP
10
Original post by BobbJo
Use sin 2A = 2sinAcosA

You'll have a quadratic in sin A.


What do i do with the cosA?
Reply 4
Avatar for Bilbao
Bilbao
OP
10
Original post by RDKGames
sin⁡(2A)−cos⁡(2A)=1\sin(2A) - \cos (2A) = 1 which is 2sin⁡Acos⁡A−cos⁡2A+sin⁡2A=cos⁡2A+sin⁡2A2\sin A \cos A - \cos^2 A + \sin^2 A = \cos^2 A + \sin^2 A

This then reduces nicely.

Ok ill try that
Original post by Bilbao
What do i do with the cosA?


You could write cos 2A = cos^2 A - sin^2 A instead, then use 1=sin^2 A + cos^2 A, the next step will become apparent
Original post by Bilbao
Sin2A -1 = Cos2A
Well im stuck
Sin2A - 1 = 1 -2 Sin^2 A
Turning it into a quadratic won't work here since Sin2A = f(2x) .
Please advice


Dear Student you can proceed as follows.
Sin2A-1 = 2Cos^2 (A) -1
2Cos^2(A) -Sin2A = 0
2 Cos^2(A) - 2SinACosA = 0
2CosA(CosA-SinA) = 0
Either CosA = 0 or CosA - SinA = 0
A = InvCos(o) or TanA = 0
A = InvTan(0)
Original post by Bilbao
Sin2A -1 = Cos2A
Well im stuck
Sin2A - 1 = 1 -2 Sin^2 A
Turning it into a quadratic won't work here since Sin2A = f(2x) .
Please advice



Original post by Bilbao
Sin2A -1 = Cos2A
Well im stuck
Sin2A - 1 = 1 -2 Sin^2 A
Turning it into a quadratic won't work here since Sin2A = f(2x) .
Please advice


Dear Student you can proceed as follows.
Sin2A-1 = 2Cos^2 (A) -1
2Cos^2(A) -Sin2A = 0
2 Cos^2(A) - 2SinACosA = 0
2CosA(CosA-SinA) = 0
Either CosA = 0 or CosA - SinA = 0
A = InvCos(o) or TanA = 0
A = InvTan(0)

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