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# Partial Fractions Watch

1. Can anyone tell me why doing two different methods yields two different answers? Thanks

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2. (Original post by Namige)
Can anyone tell me why doing two different methods yields two different answers? Thanks
Because your partial fractions break down is incomplete, and should be:

3. (Original post by ghostwalker)
Because your partial fractions break down is incomplete, and should be:

Cheers but why was my method wrong? It seems right :/

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4. (Original post by Namige)
Cheers but why was my method wrong? It seems right :/
If you plug in only two values, you'll get a solution as there are only two unknowns, when you use just A and B. It's when you try a third value, that the problem shows up.
5. (Original post by ghostwalker)
If you plug in only two values, you'll get a solution as there are only two unknowns, when you use just A and B. It's when you try a third value, that the problem shows up.
So I have used your method an have got this :

When I plug in x=4, it gives me 3x10^-5 but how can this be, as plugging it into the original formula clearly gives you zero. All other numbers work though...

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6. (Original post by ghostwalker)
If you plug in only two values, you'll get a solution as there are only two unknowns, when you use just A and B. It's when you try a third value, that the problem shows up.
I know, but why is that?

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7. (Original post by Namige)
When I plug in x=4, it gives me 3x10^-5 but how can this be, as plugging it into the original formula clearly gives you zero. All other numbers work though...
How on earth do you get 3x1o^-5?

I get 0.
8. (Original post by Namige)
I know, but why is that?

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With just A and B.

Because your values of A,B are wrong. They can never be right, because there are only two of them.

If you plug in 2 values for x, you will get values for A and B.

If you use different values for x, you will get different values for A and B.

Only when you try 3 values for x, is the problem hightlighted.
9. (Original post by ghostwalker)
How on earth do you get 3x1o^-5?

I get 0.
For the partial fractions one I get that. Every other number works fine.

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10. (Original post by Namige)
For the partial fractions one I get that. Every other number works fine.

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11. (Original post by ghostwalker)

This is for x=4.

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12. (Original post by Namige)
This is for x=4.
Should have guessed it was a calculator.

3e-15.

Well it's a problem with the accuracy of the calculator. It's stored the numbers as decimals, and all it can do is approximate the last digit.
If you can get it to work in fractions, it should come out correctly.
13. (Original post by ghostwalker)
Should have guessed it was a calculator.

3e-15.

Well it's a problem with the accuracy of the calculator. It's stored the numbers as decimals, and all it can do is approximate the last digit.
If you can get it to work in fractions, it should come out correctly.
Oh blimey. PRSOM.
14. (Original post by ghostwalker)
Should have guessed it was a calculator.

3e-15.

Well it's a problem with the accuracy of the calculator. It's stored the numbers as decimals, and all it can do is approximate the last digit.
If you can get it to work in fractions, it should come out correctly.
Doing it by Fraction in a single calculation still doesnt work, but by hand does. Very Strange.

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15. (Original post by Namige)
...
Well the problem is the calculator, or how you're using it, and not having one of that model myself, I can't help.

But the maths, by hand, is correct, 0.
16. (Original post by Namige)
Very Strange.
"Never trust a machine you can carry." Dusty Rivers
17. (Original post by ghostwalker)
Well the problem is the calculator, or how you're using it, and not having one of that model myself, I can't help.

But the maths, by hand, is correct, 0.

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