用配方法解一元二次方程(1)x2+2x-8=0 (2)x2-4=2x (3)3y2-6y-24=0 (4)4x2-7x+2=0 (5)二分之一x2-2x-9=0
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用配方法解一元二次方程(1)x2+2x-8=0 (2)x2-4=2x (3)3y2-6y-24=0 (4)4x2-7x+2=0 (5)二分之一x2-2x-9=0
用配方法解一元二次方程(1)x2+2x-8=0 (2)x2-4=2x (3)3y2-6y-24=0 (4)4x2-7x+2=0 (5)二分之一x2-2x-9=0
用配方法解一元二次方程(1)x2+2x-8=0 (2)x2-4=2x (3)3y2-6y-24=0 (4)4x2-7x+2=0 (5)二分之一x2-2x-9=0
（1）x ² + 2 x - 8 = 0
x ² + 2 x + 1 = 8 + 1
（x + 1）² = 9
x + 1 = ± 3
x = ± 3 - 1
x1 = 3 - 1 = 2
x2 = - 3 - 1 = - 4
（2）x ² - 4 = 2 x
x ² - 2 x - 4 = 0
x ² - 2 x + 1 = 4 + 1
（x - 1）² = 5
x - 1 = ± √5
x = ± √5 + 1
x1 = √5 + 1
x2 = 1 - √5
（3）3 y ² - 6 y - 24 = 0
y ² - 2 y - 8 = 0
y ² - 2 y + 1 = 8 + 1
（y - 1）² = 9
y - 1 = ± 3
y = ± 3 + 1
y1 = 3 + 1 = 4
y2 = - 3 + 1 = - 2
（4）4 x ² - 7 x + 2 = 0
x ² - （7 / 4）x + 1 / 2 = 0
x ² - （7 / 4）x + （7 / 8）² = - 1 / 2 + （7 / 8）²
（x - 7 / 8）² = - 1 / 2 + 49 / 64
（x - 7 / 8）² = 17 / 64
x - 7 / 8 = ±√17 / 8
x = ± √17 / 8 + 7 / 8
x1 = √17 / 8 + 7 / 8 = （√ 17 + 7）/ 8
x2 = - √17 / 8 + 7 / 8 = （7 - √17）/ 8
（5）（1 / 2）x ² - 2 x - 9 = 0
x ² - 4 x - 18 = 0
x ² - 4 x + 4 = 18 + 4
（x - 2）² = 22
x - 2 = ±√22
x = ± √22 + 2
x1 = √22 + 2
x2 = 2 - √22