two spherical balls lie on the ground touching . if one of the balls has a radius of 10 cm , and the point of contact is 12 cm above the ground , what is the radius of the other ball ?
"similar triangle properties . . 2 / r + 10 = 10 / r - 10 giving r = 15 / 2 . answer : d"
add(add(10, 12), 10)