(1/4)x²-2mx+n²=0
x²-8mx+4n²=0
Δ=64m²-16n²=16(4m²-n²)
√Δ=4√(4m²-n²),
由求根公式得：
x=[8m±4√(4m²-n²)]/2=4m±2√(4m²-n²)为什么△要开根号啊？在求根公式中Δ本来就在根号里面，记得
Δ本身就是：b²-4ac哦！想起来了。thanks～会做了Don't need to thank, you are very smart