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Suppose the sphere below with radius rhas a surface area equal to 45 units?Find the surface area of the sphere with twice the radius.21A. 180 units2B. 180 units3C. 90 units2D. 90 units 3

Suppose The Sphere Below With Radius Rhas A Surface Area Equal To 45 UnitsFind The Surface Area Of The Sphere With Twice The Radius21A 180 Units2B 180 Units3C 9 class=

Sagot :

Solution

It is given that the small sphere with radius r has a surface area equal to 45 units square.

The surface area of a sphere with radius r is given by;

[tex]SA=4\pi r^2[/tex]

Since the surface area of the small sphere is 45 units square.

[tex]\begin{gathered} \Rightarrow45=4\pi r^2 \\ \\ \Rightarrow\frac{45}{4\pi}=r^2 \\ \\ \Rightarrow r=\sqrt{\frac{45}{4\pi}} \end{gathered}[/tex]

To find the Surface area with twice the radius, we need to multiply the value of r by 2;

[tex]\Rightarrow R=2r=2\sqrt{\frac{45}{4\pi}}[/tex]

Therefore, the surface area is of a sphere with a radius R is

[tex]\begin{gathered} SA=4\pi R^2 \\ \\ \Rightarrow SA=4\pi(2\sqrt{\frac{45}{4\pi}})^2=4\pi(4\times\frac{45}{4\pi})=4\times45=180\text{ unit}^2 \end{gathered}[/tex]

Hence, the correct option is A.