Answer
See below.
Work Step by Step
$1+2+3+4+5=15$
$\frac{5(5+1)}{2}=\frac{5\cdot6}{2}=\frac{30}{2}=15$
Thus, they are equal.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.