Question

1、已知方程组a+b＝3.5和a-b＝1.5,求4a^2b-ab^2分之16a^2-8ab+b^2的值.

Answer 1

两个方程相加

2a=5

a=2.5,b=1

(16a^2-8ab+b^2)/(4a^b-ab^2)

=(4a-b)^2/[ab(4a-b)]

=(4a-b)/(ab)

=(4*2.5-1)/(2.5*1)

=18/5

x/(x^2-x+1)=2

2x^2-2x+2=x

2x^2-3x+2=0

把x=0代入,2=0,不成立

所以x不等于0

两边除以x

2x-3+2/x=0

x+1/x=3/2

(x+1/x)^2=x^2+2+1/x^2=9/4

x^2+1/x^2=1/4

x^2/(x^4+x^2+1)

上下同除以x^2

=1/(x^2+1+1/x^2)

=1/(1/4+1)

=4/5