Question

Two circles touch internally. The sum of their areas is 1161 sq. cm and the distance betwee
their centres is 6 cm. Find the radii of the circles.
in in the form of a rectangle ABCD in which AR = 18 cm and BC = 11 am​

Answer 1

Step-by-step explanation:

Area of 1st circle + area of 2nd circle = 116π cm²

⇒ πR² + πr² = 116π 

⇒ π(R² + r²)  = 116π

⇒ R² + r² =116 --------------------(i)

Now,

Distance between the centers of circles = 6 cm

i.e, R - r = 6

⇒  R = r + 6  -------------------(ii)

From Eqn (i) & (ii),

(r + 6)² + r² = 116

⇒ r² + 12r +36 + r² =116

⇒ 2r² +12r +36 -116 = 0

⇒ 2r² +12r - 80 = 0

⇒ r² +6r - 40 = 0

⇒ r² +10r - 4r - 40 = 0

⇒ r(r + 10) - 4(r + 10) = 0

⇒ (r + 10)(r - 4) = 0

 hence  r = 4 cm

r ≠ -10 cm        {∵ length can't be -ve}

Therefore radii of the circles are

r = 4 cm ,

R = 4 + 6 = 10 cm.