ellieee1513
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I'm really stuck with my maths homework and just wondered if anyone would be able to help me?

There are two questions that I'm stuck on (and I don't think we're allowed to use a calculator), both in the trigonometry sections to do with using the identities I think.

1. If cos B = 3/4, find the exact values of cos 2B and cos 1/2B.


2. Cos 2A = 7/18, find the possible values of Cos A and sin A.


Any help is much appreciated! Thank you
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jsMath
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(Original post by ellieee1513)
I'm really stuck with my maths homework and just wondered if anyone would be able to help me?

There are two questions that I'm stuck on (and I don't think we're allowed to use a calculator), both in the trigonometry sections to do with using the identities I think.

1. If cos B = 3/4, find the exact values of cos 2B and cos 1/2B.


2. Cos 2A = 7/18, find the possible values of Cos A and sin A.


Any help is much appreciated! Thank you
There are many ways to solve these questions, probably the easiest way would be inverse trig for you and trig identities.

recall cos2B identity and half angle identity cos 1/2B
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B_9710
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(Original post by ellieee1513)
I'm really stuck with my maths homework and just wondered if anyone would be able to help me?

There are two questions that I'm stuck on (and I don't think we're allowed to use a calculator), both in the trigonometry sections to do with using the identities I think.

1. If cos B = 3/4, find the exact values of cos 2B and cos 1/2B.


2. Cos 2A = 7/18, find the possible values of Cos A and sin A.


Any help is much appreciated! Thank you
You can use the compound angle formulae or double angle formulae in this case.
Remember that
cos2A = (cosA)^2 - (sinA)^2
Also use the double angle formulae to get half angles so
cosA = (cos(1/2A))^2 - (sin(1/2A))^2
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