·①x2+5x-1=0②2x2-4x-1=0③(1∕4)x2-6x+3=0④9(x+2)2=4(x-1)2

题目

·①x2+5x-1=0②2x2-4x-1=0③(1∕4)x2-6x+3=0④9(x+2)2=4(x-1)2

答案

①x2+5x-1=0
（x+5/2）²=1+25/4;
x+5/2=±√29/2;
x=-5/2±√29/2;
②2x2-4x-1=0
2(x²-2x)=1;
2(x-1)²=3;
x-1=±√6/2
x=1±√6/2;
;
③(1∕4)x2-6x+3=0
(1/4)(x²-24x)=-3;
x²-24x=-12;
(x-12)²=-12+144;
x-12=±√132;
x=12±2√33;
④9(x+2)2=4(x-1)2
3(x+2)=±2(x-1);
3x+6=2x-2或3x+6=2-2x;
x=-8或5x=-4；
x=-8或x=-4/5;
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