Question

设X1、X2是一元二次方程2X^2-5X+1=0的两个根，利用根与系数的关系,求下列各式的值 (要详细过)

(1)(X1-3)(X2-3)

Answer 1

x1+x2=5/2
x1x2=1/2
(1)(X1-3)(X2-3)
=x1x2-3(x1+x2)+9
=0.5-7.5+9
=2

Answer 2

x1+x2=5/2 x1x2=1/2
(X1-3)(X2-3)
=x1x2-3(x1+x2)+3
=1/2-15/2+9
=-7+9
=2

Answer 3

x1+x2=5/2 x1x2=1/2
(X1-3)(X2-3)
=x1x2-3(x1+x2)+3
=1/2-15/2+9
=-7+9
=2