Which method is NOT commonly used to solve for variables in an equation?

The reduction method is not commonly recognized as a standard technique for solving variables in an equation, especially in conventional mathematical contexts. The more widely accepted methods include the graphical method, which involves plotting equations to visualize solutions; the elimination method, where you manipulate equations to eliminate variables systematically; and the factoring method, which transforms polynomial equations into simpler forms to find roots.

The reduction method may refer to various methods in different contexts, but it doesn't align with standard terminology or widely adopted techniques used for directly solving equations in algebra or basic calculus. Therefore, the absence of this method from the typical repertoire makes it a less suitable choice compared to the others mentioned.