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Why do people say "find the integral" instead of "evaluate the integral"?

English Language & Usage Asked by Jack Tiger Lam on February 27, 2021

"find the integral" contextually implies it is some variable in some equation tucked away and you are isolating for the object somehow, which doesn’t make sense for antiderivatives, since the expression is already given. Evaluate is more appropriate since you have an expression under an operator and you want to determine the output (an integral can be viewed as an operation on a function).

The only time "find" makes sense (to me) is as the following three:

Find the integral of f(x) with respect to x / Find the integral of f(x) dx / Find ∫ f(x) dx

What I often see is this:

Find the integral ∫ f(x) dx

Expanding this as a statement, we get:

Find the integral of integral of f(x) with respect to x

which is redundant

Is this another example of Americans butchering English, given the large number of American collegiate-level mathematics textbooks out there?

One Answer

To take a trivial example, consider the function f(x)=x.

We may “find” (in the sense of determining its form) the integral function of f as I(x)=∫x.dx = x.x/2. Thus far we have only determined (found) the integral function; it has not been evaluated (in the sense of given a numerical value). That can only be done once we know the limits of x between which the integral function I(x) is to be calculated.

Hence, the integral we found may evaluate to 2 if the limits of x are (0,2), or to 6 if the limits are (2,4).

Finding is therefore a separate thing to evaluating.

Despite having no comma, your example “find the integral ∫ f(x) dx” may reasonably be understood in mathematical prose as appositional: “find the integral, ∫ f(x) dx.

Answered by Anton on February 27, 2021

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