By inspection

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By inspection is a mathematical term pertaining to the difficulty of a computation. If an expression can be evaluated by straightforward application of simple techniques (which techniques these are depends on the context) and without recourse to extended calculation or general theory, then it can be evaluated by inspection. The idea is that such computation can be done with little more than a glance at the page, hence the name.

It is also applied to solving equations; for example to find roots of a quadratic equation by inspection is to 'notice' them, or mentally check them. 'By inspection' can play a kind of gestalt role: the answer or solution simply clicks into place.