✔ 最佳答案
a² - 4ab + 5b² + 2a - 8b + 5 = 0
a² + (2 - 4b)a + 5b² - 8b + 5 = 0
a² + 2(1 - 2b)a + (1 - 2b)² + 5b² - 8b + 5 - (1 - 2b)² = 0
(a + 1 - 2b)² + 5b² - 8b + 5 - 4b² + 4b - 1 = 0
(a + 1 - 2b)² + b² - 4b + 4 = 0
(a + 1 - 2b)² + (b - 2)² = 0
因 (a + 1 - 2b)² ≥ 0 及 (b - 2)² ≥ 0
故 a + 1 - 2b = 0 及 b - 2 = 0
a = 3 及 b = 2
三角形面積為 ab/2 = 3