- #1

bigplanet401

- 104

- 0

## Homework Statement

Why does

[itex]

\int_a^b \, y \; dx

[/itex]

become

[itex]

\int_\alpha^\beta \, g(t) f^\prime(t) \; dt

[/itex]

if x = f(t) and y = g(t) and alpha <= t <= beta?

## Homework Equations

Substitution rule?

## The Attempt at a Solution

**I'm not sure how y = y(x) in the integrand turns into g(t). Isn't y a function of x in the first expression? How do they go from y(x) to g(t)?**