Question 39

The sum of radii of the two circles is 91 cm and the difference between their area is 2002 $$cm^2$$. What is the radius (in $$cm$$) of the larger circle?

Solution

We have 
$$r_1+r_2=91\ $$
and $$\pi\ \left(r_1^2-r_2^2\right)=2002$$
we get $$\ \left(r_1^2-r_2^2\right)=91\times\ 7$$
so we get $$\ \left(r_1-r_2\right)\left(r_1+r_2\right)=91\times\ 7$$
hence we know sum of radii =91 
so difference will be 7 (comparing )
Now Solving 2 equations
we get r1=49


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