问题 解答题
(1)(x+2)2=25;
(2)x2-8x+15=0;
(3)y2+2=2
2
y

(4)(x+1)(x-2)=3.
答案

(1)两边直接开平方得:x+2=±5,

则x+2=5或x+2=-5,

解得:x1=3,x2=-7;

(2 )把左边分解因式得:(x-3)(x-5)=0,

则x-3=0,x-5=0,

解得:x1=5,x2=3;

(3)移项得:y2-2

2
y+2=0,

(y-

2
2=0,

两边开方得:y-

2
=0,

则y1=y2=

2

(4)(x+1)(x-2)=3,

整理得:x2-x-5=0,

a=1,b=-1,c=-5,

x=

-b±
b2-4ac
2a
=
21
2

则:x1=

1+
21
2
x2=
1-
21
2

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