In this Q httpwwwcheggcomhomeworkhelpcalculusearlytranscend

In this Q : http://www.chegg.com/homework-help/calculus-early-transcendentals-7th-edition-chapter-6.4-problem-16e-solution-9780538497909

I don\'t get how we got (x/2) and why?

not all of us have access to that link we cant view it pls post the question directly here

$In this Q : http://www.chegg.com/homework-help/calculus-early-transcendentals-7th-edition-chapter-6.4-problem-16e-solution-9780538497909 I don\'t get how we got$