Question

What is the value of x? assume that the line is tangent to the circle

85
120
140
70

Answer 1

70°

Explanation:

Connect the center of the circle with endpoints of the chord. Let the center of the circle be point O and endpoints of the chord be points A (let point A lie on the tangent line too)and B.

From the figure, central angle AOB has the measure of 220°.

Consider triangle AOB. This triangle is isosceles triangle because OA and OB are both radii. In this triangle the measure of angle AOB is 360° - 220° = 140°.

Angles OAB and OBA are angles adjacent to the base AB, so they are congruent. The sum of the measures of all interior angles in triangle is always 180°, so

m∠OAB + m∠OBA + m∠AOB = 180°

m∠OAB = m∠OBA = 1/2 (180° - 140°)

m∠OAB = 20°

Since drawn line is tangent line, then OA is perpendicular to this tangent line and

x° = 90° - 20°

x° = 70°