Question

calculate the area of the circle. formula: $a = pi r^{2}$ use 3.14 for pi. $a = ? cm^{2}$ round to the nearest tenth.

Explanation:

Step1: Substitute the radius into the formula

Given \( r = 7\) cm and \( A=\pi r^{2}\), substitute \(r = 7\) into the formula: \(A = 3.14\times7^{2}\).

Step2: Calculate \(7^{2}\)

\(7^{2}=7\times7 = 49\). So the formula becomes \(A=3.14\times49\).

Step3: Perform the multiplication

\(3.14\times49=(3 + 0.14)\times49=3\times49+0.14\times49=147+6.86 = 153.86\).

Step4: Round to the nearest tenth

The digit in the hundredth place is \(6\). Using the rounding rule (if the digit in the hundredth place \(\geq5\), round up the digit in the tenth place), \(153.86\approx153.9\).

Answer:

\(153.9\)