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Trig Proof help needed

Tried different substitutions but im assuming i've done them incorrectly so just need some guidance on the most appropriate one to use.
35144c6d16e132780157e99923912076.png1.3KB
Reply 1
Avatar for Zacken
Zacken
22
Original post by GGHarambe
Tried different substitutions but im assuming i've done them incorrectly so just need some guidance on the most appropriate one to use.


use double angle formulas. Post what you've tried. Specifically: cos⁡2A=1−2sin⁡2A\cos 2A = 1 - 2\sin^2 A and [tex]\sin 2A = 2\sin A\cos A/tex].
Original post by GGHarambe
Tried different substitutions but im assuming i've done them incorrectly so just need some guidance on the most appropriate one to use.


Final answer is not a double angle, so the first step is to use double angle formulae for sine and cosine then manipulate it from there.
Original post by GGHarambe
Tried different substitutions but im assuming i've done them incorrectly so just need some guidance on the most appropriate one to use.


You know that tan A = sin A / cos A so that tells you to use the version of cos 2A that has just sin A in it (and be careful with the signs when you remove the brackets).
Reply 4
Avatar for GGHarambe
GGHarambe
OP
7
[QUOTE="Zacken;67621460"]use double angle formulas. Post what you've tried. Specifically: cos⁡2A=1−2sin⁡2A\cos 2A = 1 - 2\sin^2 A and sin⁡2A=2sin⁡Acos⁡A/tex].\sin 2A = 2\sin A\cos A/tex].

1-(1-2sin^2)/sin 2A

-2Sin^2/Sin 2A

-2sin^2/SIN A Cos A + Sin A Cos A
Original post by GGHarambe
1-(1-2sin^2)/sin 2A

-2Sin^2/Sin 2A

-2sin^2/SIN A Cos A + Sin A Cos A


You expanded wrong, 1−(1−2sin⁡2(A))≠−2sin⁡2(A)1-(1-2\sin^2(A)) \not= -2\sin^2(A). Check it again.

Denominator looks good.
(edited 7 years ago)
Reply 6
Avatar for GGHarambe
GGHarambe
OP
7
Original post by RDKGames
You expanded wrong, it should be +sin⁡2(A)+\sin^2(A). Check it again.

:mad: Thanks
Reply 7
Avatar for GGHarambe
GGHarambe
OP
7
Original post by RDKGames
You expanded wrong, 1−(1−2sin⁡2(A))≠−2sin⁡2(A)1-(1-2\sin^2(A)) \not= -2\sin^2(A). Check it again.

Denominator looks good.


How come it's not 2Sin^2 ?
Original post by GGHarambe
How come it's not 2Sin^2 ?


Huh?
Reply 9
Avatar for GGHarambe
GGHarambe
OP
7
Original post by RDKGames
Huh?


originally you put +Sin^2 and i'm where has the 2 in front gone
Original post by GGHarambe
originally you put +Sin^2 and i'm where has the 2 in front gone


Simple error that I fixed and you came back too quickly for.
Reply 11
Avatar for GGHarambe
GGHarambe
OP
7
Original post by RDKGames
Simple error that I fixed and you came back too quickly for.


Oh okay my bad. Thought I was going insane.
Original post by GGHarambe
1-(1-2sin^2)/sin 2A

-2Sin^2/Sin 2A

-2sin^2/SIN A Cos A + Sin A Cos A


I did say be careful with the signs when you remove the brackets!

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