1 1 1
x ² - ( — ) ² = ( x + — ) × ( x - — )
x x x
是因式分解.
1 1 1 1
x ² - ( — ) ² = x ² + x ×— - x × — - ( — ) ²
x x x x
1 1
= ( x + — ) × ( x - — )
x x