The area of the region is equal to the area under the curve <em>y</em> = cos(<em>x</em>) over the interval 0 ≤ <em>x</em> ≤ <em>π</em>/6, given by the integral
which follows from
• the fact that d/d<em>x</em> [sin(<em>x</em>)] = cos(<em>x</em>)
• the fundamental theorem of calculus