Author Topic: tignometry query  (Read 1418 times)

Offline spiderman

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tignometry query
« on: September 15, 2009, 11:50:36 am »
Prove the following identity

(1-2sin^2@)/(cos@+sin@)==cos@-sin@


Pls help someone
« Last Edit: September 15, 2009, 12:28:50 pm by spiderman »
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Offline Ghost Of Highbury

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Re: tignometry query
« Reply #1 on: September 15, 2009, 12:15:42 pm »
Prove the following identity

(1-2sin^2@)/(cos@+sin@)==cos@=sin@


Pls help someone
wats the "=="

and how can cos @ = sin @
is the q correct?
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Offline spiderman

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Re: tignometry query
« Reply #2 on: September 15, 2009, 12:19:10 pm »
== means that we have to solve the left hand side to get an answer matching the rhs
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Offline astarmathsandphysics

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Re: tignometry query
« Reply #3 on: September 15, 2009, 12:21:47 pm »
think the rhs should be cos@-sin@
multuply both sides by cos@+sin@ to get
1-2sin2@=(cos@+sin@)(cos@-sin@)=cos2@-sin2@=cos2@

1-2sin2@=cos2@ is an identity

Offline Ghost Of Highbury

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Re: tignometry query
« Reply #4 on: September 15, 2009, 12:21:59 pm »
wats the "=="

and how can cos @ = sin @
is the q correct?

ok..i assume this is the question

(1-2sin^2@)/(cos@+sin@)= cos@ - sin@

the answer-----------

1 - 2sin2@ = sin2@ + cos2@ - 2sin2@ = cos2@ - sin2@

cos2@ - sin2@ = (cos @ + sin @) (cos @ - sin @)

wen u divide it by (cos@+sin@)

it is = (cos @ + sin @) (cos @ - sin @) / (cos@+sin@) = (cos @ - sin @)

therefore LHS = RHS

is this the question?
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Offline spiderman

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Re: tignometry query
« Reply #5 on: September 15, 2009, 12:28:30 pm »
Tahnks ssooo much
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Offline spiderman

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Re: tignometry query
« Reply #6 on: September 15, 2009, 12:39:55 pm »
Please can someone help me with the 4th question in the attached past paper
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Offline astarmathsandphysics

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Re: tignometry query
« Reply #7 on: September 15, 2009, 12:49:31 pm »
i)The equilibrium is at y=3. c=3, the displacement of the curve from equilibrium. The amplitude a =6 and the perid from the gaph is pi so b=2pi/pi=2

ii)y=0 so 6sin(2x)+3=0 so sin(2x+3)=-0.5 so
2x=sin-1-0.5=-30

2x=180--30=210 x=105
2x=360+-30=330 so x=165
2x=540--30=570 so x=285
2x=720+-30=690 so x=345

Offline spiderman

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Re: tignometry query
« Reply #8 on: September 15, 2009, 12:52:39 pm »
Thank you so much astar
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