The circle shape, its area is the second power of 200cm, the outer radius of the big circle is 10cm, the inner radius of the small circle is what? Solve by equation

The circle shape, its area is the second power of 200cm, the outer radius of the big circle is 10cm, the inner radius of the small circle is what? Solve by equation

Let it be r
(10 ` 2-r ` 2) Pai = 200
It's about six

Circular ring, its area is 200 cm square, the radius of the big circle is 10 cm, what is the radius of the inner circle?

s=S1-s1
=∏R^2-∏r^2
=3.14(10×10-r^2)=200
r≈6.025cm

When the edge length of a cube increases to 5 times, the surface area and volume of the cube increase to () times and () times respectively

Analysis:
Suppose that the original edge length is a, then 5 times larger is 5A,
The original surface area S1 = a * a * 6 = 6A & sup2;,
Now surface area S2 = (5a) * (5a) * 6 = 25 * 6A & sup2;,
Therefore, the surface area expansion ratio is 25 * 6A & sup2 / 6A & sup2; = 25, that is 25 times,
The original volume V1 = a * a * a = a ^ 3,
Now volume V2 = (5a) * (5a) * (5a) = 125A ^ 3,
Therefore, the volume expansion multiple is 125 A ^ 3 / A ^ 3 = 125, that is 125 times
I hope I can help you