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#1

$Old$ November 19th, 2009, 07:19 AM

Oasis1993 $Oasis1993 is offline$

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$Default$ sin a sinx+ b cosx

Hey.
The question is find the value of R and the value of A.

sinx+ 2cosx = Rcos(x-A)

i can find R which is square root of 5, but i keep getting 1.11 for A and the answer is 0,46 (radians)

can anyone help?

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#2

$Old$ November 19th, 2009, 08:35 AM

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Hello Oasis1993

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Originally Posted by Oasis1993 $View Post$

Hey.
The question is find the value of R and the value of A.

sinx+ 2cosx = Rcos(x-A)

i can find R which is square root of 5, but i keep getting 1.11 for A and the answer is 0,46 (radians)

can anyone help?

$R\cos(x-A) = R\cos x \cos A + R \sin x \sin A=\sin x + 2\cos x$

$\Rightarrow R\sin A = 1,\;R\cos A = 2$

$\Rightarrow \tan A =\tfrac12$

$\Rightarrow A = 0.46...$

Grandad

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