Assignment V equality (was: Bliss was Re: DEC program listing

Fred Cisin cisin at
Wed Aug 17 18:59:36 CDT 2005

On Wed, 17 Aug 2005, Tony Duell wrote:
> Thrivial example... On most (if not all) calculators, try something like
> 1 E 20 [enter] 1 + 1 E 20 -
> (Ooops, that's in RPN, I've forgotten how to do it on a normal
> calculator, try soemthing like 1 E20 + 1 = - 1 E 20 = )
> Explain why the result is not 1 (OK, we all know the answer here...)

An excellent example.  Unfortunately, some of them are using cereal box 4
function calculators, some of which won't permit input of 1E20, and may
require different values from one to another.

Hmmmm!  If I come up with a similar simple example using the WINDOZE
calculator, then I can kill two birds with one stone.

(I think they fixed the bug in the Windoze calculator that caused the
Windoze 3.1 calculator to come up with 3.11 - 3.10 => 0)

> > Then take the number that you wrote down (0.3333333) and multiply it by 3.
> > EXPLAIN what is wrong with the calculator to not give 1.0."
> And hope nobody has an HP49, which does this _symbolically_ and gives the
> exact answer...
> More interesting, why do some lesser calculators apparently give the
> right answere if you do 1 / 3 = * 3 = ? And why do I object to such
> designs ?

part of why I include the "extraneous" "write it down and turn off the
calculator for 24 hours"

> For non-negative numbers, sqrt and x^2 are inverse operations. Enter any
> number, take the sqaure root 100 times in succession. Now square the
> result of that 100 times. For numerical (as opposed to symbollic)
> calculators, you'll get an answr of 0 for inputs such that 0<=x<1, and 1
> for inputs such that x>=1.

Some of them do just fine and understand what is going on with squaring a
square root.  But some of them have SO little actual understanding of math
that they don't get it.

Teaching beginners is incredibly frustrating.
But it makes it all worthwhile if/when they understand.
... and it is FANTASTIC when when SOME of them over the years go on to
exceed my [admittedly very limited] abilities!

Grumpy Ol' Fred     		cisin at

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