习题2.3 (1)x^2+12x+25=0 (2)x^2+4x=10 (3)x^2-6x=11 (4)x^2-2x-4=
3个回答

解(1):x²+12x+25=0

x²+12x=-25

x²+12x+36=-25+36

(x+6)²=11

x+6=±√11

x+6=√11或x+6=-√11

x1=-6+√11, x2=-6-√11

(2):x²+4x=10

x²+4x+4=10+4

(x+2)²=14

x+2=±√14

x+2=√14或x+2=-√14

x1=-2+√14, x2=-2-√14

(3):x²-6x=11

x²-6x+9=11+9

(x-3)²=20

x-3=±√20

x-3=±2√5

x-3=2√5或x-3=-2√5

x1=3+2√5, x2=3-2√5

(4):x²-2x-4=0

x²-2x=4

x²-2x+1=4+1

(x-1)²=5

x-1=±√5

x-1=√5或x-1=-√5

x1=1+√5, x2=1-√5