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2x"-5x+2=0配方法

2x^2+5x-4=0 x^2+(5/2)x=2 x^2+(5/2...2009-08-14 用配方法证明x^2-5x+7的值恒大于零...

2x^2-5x+2=0 x^2-5/2x+1=0 x^2-5/2x+(5/4)^2 -(5/4)^2 +1=0 (x-5/4)^2 =9/16 x-5/4 =3/4或x-5/2 =-3/4 x=2或x =1/2

2x^2-5x+3=0 2(x²-5x/2)+3=0 2(x-5/4)²+3-25/8=0 2(x-5/4)²=1/8 (x-5/4)²=1/16 x-5/4=±1/4 x=1或x=3/2 十字相乘法 2x^2-5x+3=0 (2x-3)(x-1)=0 x=1或x=3/2

2x^2-5x+1=0 2(x^2-5x/2+25/16)-25/8+1=0 2(x-5/4)^2=17/8 (x-5/4)^2=√17/16 x-5/4=±√17/4 x=±√17/4+5/4

(2x+1)(x+2)

2x²-5x-1=0 解:x²-5/2x-1/2=0(先将x²的系数变为1) x²-5/2x+(5/2÷2)²-1/2-(5/2÷2)²=0(通过x²和x的系数来决定平方和或平方差的常数项) x²-5/2x+25/16-33/16=0 x²-5/2x+25/4=33/16(两边同...

2x²+2√5x+1=0 2(x²+√5x+(√5/2)²)-2(√5/2)²+1=0 2(x+√5/2)²=3/2

(1)2x2+5x-3=0,2x2+5x=3,x2+52x=32,配方得:x2+52x+(54)2=32+(54)2,(x+54)2=4916,开方得:x+54=±74,x1=13,x2=-3; (2)5x+2=3x2,3x2-5x-2=0,b2-4ac=(-5)2-4×3×(-2)=49,x=5±492×3,x1=2,x2=-13;(3)2x(x-3)=5(x-3)...

2(x^2+5x/2)+4=0 (x^2+5x/2+25/16)=-2+25/16 (x+5/4)^2=-7/16 所以x在实数范围内无解!

解:(1)x 1 =-1,x 2 = ; (2)x 1 =4 , ; (3)x 1 =4,x 2 =- 。

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