Question

the area of a the ring between the two concentric circles is 3168cm² .find the radii of the two circles if( (i) their sum is 42 (ii ) their difference is 28 cm

Answer 1

Let these radii be x and y
A. T. Q.
x + y= 42 - - - - - equation 1
x- y =28 - - - - - - - - equation 2
Adding both equations...
2x=70
x= 35 cm
and put this in 2
35-y =28
y= 35-28
y=7 cm