Bonjour
Chllloeh
La somme des mesures des angles d'un triangle est égale à 180°.
∡BAC + ∡BCA + ∡ABC = 180°
∡BAC + ∡BCA + 90° = 180° car le triangle ABC est rectangle en B
∡BAC + ∡BCA = 180°- 90°
∡BAC + ∡BCA = 90°
Or ∡BAC = 3 * ∡BCA
Donc
3 * ∡BCA + ∡BCA = 90°
4 * ∡BCA = 90°
∡BCA = 90°/4
∡BCA = 22,5°
Donc ∡BAC = 3 * ∡BCA
= 3 * 22,5
= 67,5°
Par conséquent :
∡BCA = 22,5°
∡BAC = 67,5°
∡ABC = 90°