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**Abbas0000****Member**- Registered: 2017-03-18
- Posts: 29

I thought that you can help me with this. I've seen this in some textbook and I don't know how do thay measured the product of equation ;

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,452

hi Abbas0000

The book result comes straight from the quadratic formula http://www.mathsisfun.com/algebra/quadr … ation.html

But your result is the same. You just have a negative on both sides of the book version.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob Bundy

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**Abbas0000****Member**- Registered: 2017-03-18
- Posts: 29

Thanks but I can't understand how is( x ) multiplyed by( r)?

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**bob bundy****Administrator**- Registered: 2010-06-20
- Posts: 8,452

hi Abbas0000

Arh, I understand your confusion. This result does work for this quadratic, but is not true in general. If you multiply out the expression you'll see that it is true.

The reason is that r1 and r2 are reciprocals; ie. r1 = 1/r2 and r2 = 1/r1

If you make that substitution you'll see that the expression becomes (1-r1)(1-r2) which is what you have.

Hopefully that's enough for you to sort this out. I'm in a rush right now, but I'll post more details later if you need.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob Bundy

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