If radius of a circle is 3cm, what is the area of the circle in sq. cm.? [Indian Railway Gr. 'D' Exam, 2014]

### Concept & Area of a Circle The area of a two-dimensional circle is determined by squaring its radius and multiplying by Pi ($\pi$). $$Area = \pi r^2$$ ### Step-by-Step Solution * Given: The radius ($r$) of the circle is 3 cm. * The formula for the area of a circle is $Area = \pi r^2$. * Substitute the given radius into the formula: $Area = \pi \times (3)^2$. * Calculate the square of 3, which is 9. * Therefore, the area is $9\pi$ sq. cm. ### Exam Strategy & Shortcut For simple radius values, simply square the number mentally and attach $\pi$. Since $3^2 = 9$, the answer is instantly $9\pi$. Do not convert $\pi$ to $\frac{22}{7}$ unless the options are given in standard numerical format. ### Common Pitfall A frequent mistake is calculating the circumference instead of the area ($2\pi r = 6\pi$), or forgetting to square the radius. ### Final Answer Therefore, the correct answer is **$9\pi$**.