Explanation
The area of a portion of a circle with radius 'r' and central angle 'a' in radians is:
[tex]A_{\text{portion}}=\frac{1}{2}\cdot r^2\cdot a[/tex]
In this problem, the radius is r = 4cm, and the angle a = 30º.
First we have to express the angle in radians:
[tex]a=30º\cdot\frac{\pi}{180º}=\frac{1}{6}\pi[/tex]
And now we can find the area of the shaded region:
[tex]\begin{gathered} A=\frac{1}{2}\cdot(4\operatorname{cm})^2\cdot\frac{1}{6}\pi \\ A=\frac{1}{2}\cdot16\operatorname{cm}^{2}\cdot\frac{1}{6}\pi=\frac{4}{3}\pi \end{gathered}[/tex]
Answer
The area of the shaded region is:
[tex]A=\frac{4}{3}\pi cm^{2}[/tex]
