If two tangents inclined at an angle 60° are drawn to a circle of radius 5 cm, then what is the length of each tangent?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → $5\sqrt{3}$ cm
Given: Two tangents are drawn to a circle of radius 5 cm, and the angle between the tangents is $60^\circ$.
Each tangent forms a right-angled triangle with the radius (tangent is perpendicular to radius at the point of contact).
Draw radii to the points of contact. The angle between the radii is $180^\circ - 60^\circ = 120^\circ$ because the tangents meet outside the circle and subtend an angle of $60^\circ$.
So, each triangle formed is an isosceles triangle with two sides of length $r = 5$ cm and the included angle = $120^\circ$.
Use the Cosine Rule to find the length of the tangent (side opposite $120^\circ$):
$l^2 = r^2 + r^2 - 2r^2\cos(120^\circ)$
$l^2 = 25 + 25 - 2 \cdot 25 \cdot \cos(120^\circ)$
$\cos(120^\circ) = -\frac{1}{2}$
$l^2 = 50 + 25 = 75$
$l = \sqrt{75} = 5\sqrt{3}$