Question

what method of factoring should first be used?

u - 1

answer
greatest common factor difference of perfect squares
trinomial factoring none of the above

Explanation:

The expression $u-1$ is already in its simplest factored form. It cannot be factored using the Greatest Common Factor (there is no common factor other than 1), it is not a difference of perfect squares (which requires the form $a^2 - b^2$), and it is not a trinomial (which has three terms).

Answer:

None of the Above