Here is the equation that i've made \begin{align*} S&=\pi R^2\\ S_1&=\pi {R_1}^2\left(\frac{24}{360}\right)\\ S_2&=\pi{R_2}^2\left(\frac{24}{360}\right) \end{align*}

then, \begin{align*} S_1-S_2&=\text{ shaded area}\\ S_1-S_2&= \pi {R_1}^2\left(\frac{24}{360}\right)-\pi {R_2}^2\left(\frac{24}{360}\right)\\ &= \pi 4^2\left(\frac{24}{360}\right)-\pi 1^2\left(\frac{24}{360}\right)\\ &= 16\pi \left(\frac{24}{360}\right) - \pi \left(\frac{24}{360}\right)\\ &= \frac{16}{15}\pi -\frac{1}{15}\pi\\ &=\pi \end{align*} Answer: $\pi$

I feel my equation is wrong, but I don't know what's wrong with it.

Also, i am wondering the way to do this kind of question is changing the area degree to radiuss first or we dont need to.

• sorry I forgot to upload my picture, now here it is! – Momoko Jan 29 '14 at 20:57
• @RossMillikan My bad, thanks! I am always bit worried while I am doing some edit, that I will miss something. Sometimes I just go through few questions in my spare time. Should have paid more attention to what I was doing! – quapka Jan 29 '14 at 22:52