"John Rumm" wrote in message
news
On 06/06/2015 19:07, tim..... wrote:

"Farmer Giles" wrote in message
...
On 06/06/2015 11:15, tim..... wrote:

"Tim Streater" wrote in message
.. .
In article , Tim Watts
wrote:

Prove that: n^2-n-90=0

For n = -9 or n = 10, easy enough to do in one's head.

That's a solution

not a proof

tim




Correct, it is not a proof - neither was my answer earlier.

This is, though: 6/n x 5/n-1 = 1/3

-- 30/n^2-n = 1/3

-- 90 = n^2-n -- 0 = n^2-n-90

but it's still not a proof in the context of a maths question, which is

prove that n = 10 (from the information in the question, not from the
equation)

There is no requirement to "prove" n=10

You are misunderstanding the way that "proof" in mathematics works.

You have been asked for a proof, so in order to get the marks you first have
to find something that you can "prove".

Simply using the equation to solve n=10 isn't it, because that is not a
proof.

And as the equation resolved down to n=10 the thing that you have, that can
be proved, is that n=10 is, in fact, the solution to the narrative part of
the question.

Thus there becomes a requirement to prove that n=10 solves the sweet
problem, because that's all you have that you can use as the result of a
mathematical proof.

(and finding that n=10 would be finding a solution, not providing a proof)

Correct, so it's can't be the solution to the question that gets you the
marks

tim