（1）x ² - 25 = 0
x ² = 25
x = ± 5
（2）4（x + 1）² = 81
（x + 1）² = 81 / 4
x + 1 = ± 9 / 2
x = ± 9 / 2 - 1
（3）4 x ² = 64
x ² = 16
x = ± 4
（4）x ² / 2 - 98 = 0
x ² / 2 = 98
x ² = 196
x = ± 14