Science:Math Exam Resources/Courses/MATH110/April 2012/Question 03 (b)/Statement

Consider a function ƒ whose derivative is equal to 0 on the entire interval $(-\infty ,\infty )$. Let x₁ and x₂ be two points on $(-\infty ,\infty )$. Prove, using your answer in part (a), that

$\displaystyle f(x_{2})-f(x_{1})=0.$