Two common tangents AC and BD touch two equal circles equal of radius 7 cm, at points A, C, B and D, respectively, as shown in the figure . If the length of BD is 48 cm, what is the length of AC ?
Answer & explanation
Correct answer: option 3
AC = Length of the direct common tangents
BD = Length of direct transverse tangents
Let, the distance between two circles = x cm
So, BD = √(\( { x}^{2 } \) - \( { 7\; +\; 7}^{2 } \))
⇒ 48 = √(\( { x}^{2 } \) - \( { 14}^{2 } \))
Squaring both sides
⇒ \( { 48}^{2 } \) = \( { x}^{2 } \) - 196
⇒ 2304 = \( { x}^{2 } \) - 196
⇒ \( { x}^{2 } \) = 2304 + 196 = 2500
⇒ x = \(\sqrt {2500 }\) = 50 cm
ALso AC = √(\( { 50}^{2 } \) - \( { 7\; -\; 7}^{2 } \))
⇒ AC = \(\sqrt {2500 }\) = 50 cm
Therefore, the length of BD is 48 cm and AC is 50 cm.