2024 · Q35
Let ABC be a triangle with area 36 square cm. If AB = 9 cm, BC = 12 cm and ∠ABC = θ, then what is cos θ equal to?
Elementary MathematicsGeometry: Lines, Angles and Triangles
- A53
- B54
- C1/3
- D2/3
Explanation
Area = ½·AB·BC·sinθ = ½×9×12×sinθ = 36 gives sinθ = 2/3. Then cosθ = √(1−4/9) = √5/3 (θ acute). This is option A (stored label '53' = √5/3).