Question about Texas Instruments TI-86 Calculator

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Multiplication error(?) with repeating decimal place fractions.

When I enter 7*(-1/7)+1
I get a return of 2E-14

BUT
When I enter 7*-1/7+1
I get the expected return of 0

It is a problem with fractions that have repeating decimals and does not exist with fractions that terminate.

i.e.
6*(-1/6)+1
answer comes in as expected, at zero

What gives?

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Hello,
You may have guessed right. The presence of the parentheses makes the content of the parentheses evaluated first. So there is a loss of precision.
On the Ti92 I do 7*(-1/7)+1 and find 0.
But with Floating mode set at 12 decimal digits I get
1/7.=.142857142857.
Then .142857142857.*(-7) + 1 gives 2E-14.
Try to calculate pi*(-1/pi) +1 or e*(1/e)+1.
Hope it answers your question.

Posted on Sep 23, 2009

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