What is the condition for two circles to touch each other internally?
d=r1+r2d = r_1 + r_2d=r1+r2
d=∣r1−r2∣d = |r_1 - r_2|d=∣r1−r2∣
d<r1+r2d < r_1 + r_2d<r1+r2
d=0d = 0d=0