kathyishappy
幼苗
共回答了19个问题采纳率:89.5% 举报
(1)∵
1
2 (2x+1) 2 =36,
∴(2x+1) 2 =72,
∴2x+1=±6
2 ,
解得:x 1 =3
2 -
1
2 ,x 2 =-3
2 -
1
2 ;
(2)∵x 2 +3x=0,
∴x(x+3)=0,
即x=0或x+3=0,
解得:x 1 =0,x 2 =-3;
(3)∵9=x 2 -2x+5,
∴x 2 -2x=4,
∴x 2 -2x+1=5,
即(x-1) 2 =5,
∴x-1=±
5 ,
解得:x 1 =1+
5 ,x 2 =1-
5 ;
(4)∵a=3,b=2,c=-3,
∴△=b 2 -4ac=4-4×3×(-3)=40,
∴x=
-b±
△
2a =
-2±2
5
2×3 =
-1±
5
3 .
1年前
4