2015 · Q68
The two adjacent sides of a cyclic quadrilateral are 2 cm and 5 cm and the angle between them is 60°. If the third side is 3 cm, then the fourth side is of length
Elementary MathematicsCircles
- A2 cm
- B3 cm
- C4 cm
- D5 cm
Explanation
AC^2 = 2^2 + 5^2 - 2*2*5*cos60 = 19; with angleD = 120 deg, 19 = 3^2 + x^2 - 2*3*x*cos120 gives x^2 + 3x - 10 = 0, so x = 2 cm. Hence option (a).