The radius of a circle is 7 cm. Determine the radius of another circle whose area is 9 times of the first circle.  Ops:   A. 212 cm    B. 21 cm    C. 162 cm    D. 16 cm

The area of a circle is given by the formula πr², where r is the radius of the circle.

Step 1: Find the area of the first circle. The radius of the first circle is given as 7 cm. So, its area is π*(7 cm)² = 49π cm².

Step 2: Find the area of the second circle. The area of the second circle is 9 times the area of the first circle. So, its area is 9*49π cm² = 441π cm².

Step 3: Find the radius of the second circle. We know that the area of the second circle is 441π cm². We can set this equal to πr² and solve for r: 441π cm² = πr² Divide both sides by π: 441 cm² = r² Take the square root of both sides to solve for r: r = √441 cm = 21 cm

So, the radius of the second circle is 21 cm. The correct answer is B. 21 cm.