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#1

$Old$ October 9th, 2008, 11:02 AM

Flexible $Flexible is offline$

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$Default$ Help please!!!!

How do i expand this:

-2 x (x+1) x (2-x) x cos120

Thanks,

F.

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$Old$ October 9th, 2008, 11:09 AM

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$Default$ -2 x (x+1) x (2-x) x cos120

cos 120=-1/2...so when you multiply the -2 by -1/2..you get one
so now you have (x+1)(2-x)=2x-x(squared)+2-x
=-x(squared)+x+2

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$Old$ October 9th, 2008, 11:17 AM

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Originally Posted by Flexible $View Post$

How do i expand this:

-2 x (x+1) x (2-x) x cos120

Thanks,

F.

Don't use "x" for multiplication. It's confusing.

$-2x(x+1)(2-x)\cos120$

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$Old$ October 9th, 2008, 11:18 AM

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ah ok thanks what happens when you have cos45? For example;

- 2 x (x+2) x 4 x cos45.

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$Old$ October 9th, 2008, 11:21 AM

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$Default$ ah ok thanks what happens when you have cos45? For example; - 2 x (x+2) x 4 x cos45.

cos45=((square root)2)/2 when you multiply by -2..you will have -(square root)2
=4x+8-(square root)2

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$Old$ October 9th, 2008, 11:36 AM

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I'm stuck! I'm trying to find x using the cosine rule from:

$7^2=(x+2)^2 + 4^2 - 2 \ (x+2) \ 4 \ cos45$

The answer is; x = 7.23 from:

$x^2 - 4(\sqrt2 - 1)x - (29 + 8\sqrt2) = 0$

Last edited by Flexible; October 9th, 2008 at 12:12 PM.

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