X（x-1）➗2＝15 X*（x-1）/2=15
x(x-1)/2=15\u600e\u4e48\u89e3?\u8981\u6700\u8be6\u7ec6\u7684\u89e3\u6cd5\uff0c\u4e00\u6b65\u4e00\u6b65\u89e3x(x-1)/2=15
x(x-1)=30
x²-x-30=0
(x+5)(x-6)=0
x+5=0\u6216x-6=0
x1=-5
x2=6
x²-x=30
x²-x-30=0
(x-6)(x+5)=0
x=6,x=-5
方法如下，
请作参考：
x1=6，x2=-5
解：x（x―1）÷2＝15
x²―x＝30
（x―1/2）²＝30+1/4＝121/4
x―1/2＝±11/2
x1＝11/2+1/2＝6
x2＝―11/2+1/2＝―5
两边同时乘以2
x(x-1)＝30
去括号，移项，变形为
x^2-x-30=0
因式分解
（x-6）(x+5)=0
所以解得
x＝6或x＝-5
解:x(x-1)÷2=15
x(x-1)=30
xx-x-30=0
(x+5)(x-6)=0
x+5=0
x1=-5
x-6=0
x2=6
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