x²-6x+18因式分解

” - 4ac = 36 - 72 < 0,
方程 x" - 6x + 18 = 0 无实数解,
分解因式,
就只能复数范围有结果,
x” - 6x + 18
= x" - 6x + 9 + 9
= ( x - 3 )" + 3"
= ( x - 3 )” - (3i)”
= ( x - 3 - 3i )( x - 3 + 3i )