Two circles intersect at two points. Which of the following statements is true?
- (a)The internal tangent is longer than the external tangent
- (b)Only two common tangents exist
- (c)The number of tangents depends on radii
- (d)They must be concentric
Answer
Why
Correct — B. Count the common tangents from how the circles sit.
A transverse tangent keeps the two circles on opposite sides of it. Intersecting circles share points, so no transverse tangent exists.
The two direct tangents, with both circles on the same side, still exist.
Total: 2 common tangents → option (b)
Why the others are wrong
- (a)The internal tangent is longer than the external tangent — Intersecting circles have no internal (transverse) tangent to compare. An internal tangent keeps one circle on each side of it, which is impossible once the circles overlap.
- (c)The number of tangents depends on radii — The count is fixed by position, not by radii alone: it depends on the centre distance d against r₁ + r₂ and r₁ − r₂. Any two circles cutting at two points have 2.
- (d)They must be concentric — Concentric circles never cut at two points: unequal radii give no common point and equal radii give the same circle. Intersecting circles must have different centres.
Concept
Count common tangents from d, the distance between the centres, taking r₁ > r₂.
d > r₁ + r₂ (apart): 4, two direct and two transverse
d = r₁ + r₂ (touching outside): 3
r₁ − r₂ < d < r₁ + r₂ (intersecting): 2, both direct
d = r₁ − r₂ (touching inside): 1
d < r₁ − r₂ (one inside the other): 0
Direct (external) tangents have both circles on the same side of the line. Transverse (internal) tangents cross the line of centres with one circle on each side, so they exist just when the circles do not overlap.
Key facts
- Two circles cutting at two points have exactly 2 common tangents, both direct.
- Circles touching externally have 3 common tangents, circles touching internally have 1.
- Circles lying apart (d > r₁ + r₂) have 4: two direct and two transverse.
Study next
Common traps
- Answering 4 by reflex — that count belongs to circles lying apart, not intersecting ones.
- Counting the common chord through the two intersection points as a tangent — it cuts both circles, so it is a secant.
Counting tangents from position also decides 17 Sep 2025, 12:30, Quant Q.21: radii 6 and 2 with centres 10 apart give d > 8, so 4 tangents.
15 Sep 2025, 12:30, Quant Q.22 asks about circles touching internally (1), and 23 Sep 2025, 09:00, Quant Q.21 asks for exactly three tangents, which needs d = 5 + 3 = 8 cm.
Related PYQs
No directly related past PYQ was found.