at the l.l.a. examination

In Algebra, if Algebra be ours,
x and x2 can ne'er be equal powers,
Unless x=1, or none at all.

It is the little error in the sum,
That by and by will make the answer come
To something queer, or else not come at all.

The little error in the easy sum,
The little slit across the kettle-drum,
That makes the instrument not play at all.

It is not worth correcting: let it go:
But shall I? Answer, Prudence, answer, no.
And bid me do it right or not at all.