Circles Area

[Psychguy98]

By what number is the area of a circle multiplied if its radius is doubled?

I know we use A= pi r^2 .

 

[tkhunny]

Try substitution. r = 2R

 

[Psychguy98]

Area of original circle can be pi x^2. The area of new circle pi(2x)^2 = ? Like that?

 

[tkhunny]

Yes. Now do your best to make it look like like what you started with.

 

[Psychguy98]

so pi(2x)^2 = 4pi x^2 ?

 

[Deleted member 4993]

so pi(2x)^2 = 4pi x^2 ?

Now - what was the original area of the circle (before doubling the radius)?

 

[Psychguy98]

is it pi x^2?

 

[Deleted member 4993]

is it pi x^2?

Yes - now think about how you are going to synthesize all these information and get your answer (the most important part of problem solving)

 

[tkhunny]

It would be more obvious if you had used "R" rather than "x". Try to avoid the pathological usage of 'x'. Pick names that are more meaningful.

\(\displaystyle \pi r^{2}\) relates how to \(\displaystyle 4\cdot \pi R^{2}\)

 

[Psychguy98]

multiplied by 4?

 

[tkhunny]

I told you it was obvious. :wink: