你好!
ax² + bx + c = 0 (a≠0)
ax² + bx = - c
x² + bx/a = -c/a
x² + bx/a + (b/2a)² = (b/2a)² - c/a
(x + b/2a)² = (b² - 4ac) / (4a²)
x + b/2a = ± √(b² - 4ac) / 2a
x = [ -b ±√(b² - 4ac) ] / (2a)
例：用配方法解方程 2x² + 4x - 3 = 0
2x² + 4x - 3 = 0
2x² + 4x = 3
x² + 2x = 3/2
x² + 2x+1 = 3/2 + 1
(x+1)² = 5/2
x+1 = ±√(5/2)
x = - 1±√(5/2)
x = (- 2 ± √10) /2