x²-8x+4=0解方程，用公式法，x=[8±√(64-16)]/2=4±2√3
x=[8±√(8²-4*4)]/2=4±2√3
解：x²-8x=-4x²-8x+16=-4+16(x-4)²=12x-4=±2√3∴x=4 ± 2√3
x²-8x+16+4-16=0(x-4)²=12
