Question

In a expression surface area = 4πr2 ,factor of 4 is exact number. how many s. f are there in factor 4?

Answer 1

Given Area of the base of a hemisphere is 3 = PI * R^2  

Thus R = Sqrt ( 3 / PI ) .  

Surface area of whole sphere = 4*PI*R^2 .  

= 4 * PI * 3 / PI  

= 12 .  

Since the hemisphere is half of a sphere the Surface area of the hemisphere = 12 / 2  

= 6 ( curved part , not including the flat rounded base ) .  

But the total surface area = 6 + Area of the base of a hemisphere .  

= 6 + 3  

= 9.

Answer 2

Hey !

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In the expression surface area is

$4π{r}^{2}$

The factor 4 is an exact number - which has infinite number of significant figures .

It can be written as 4 or

4 . 0 or 4 .00 or 4 . 000 n so on .

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