find radius of circle

Question

the area of circle varies directly as square of its radius.find the radius of circle whose area is equal to the sum of the areas of two circles whose radii are 5 cm and12 cm

Answer 1

serkel, area

serkel 1: rad=5

serkel 2: rad=12

want tu get serkel3 with area=sum av abuv 2 area

serkel area=pi*rad^2

rad3=root(5*5 +12*12)

red3=13