设方程4x²-7x-3=0的两个根为:x1,x2,不解方程,求下列各式的值x1²+x2² (x1-3)(x2-3)
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设方程4x²-7x-3=0的两个根为:x1,x2,不解方程,求下列各式的值x1²+x2² (x1-3)(x2-3)
设方程4x²-7x-3=0的两个根为:x1,x2,不解方程,求下列各式的值
x1²+x2² (x1-3)(x2-3)
设方程4x²-7x-3=0的两个根为:x1,x2,不解方程,求下列各式的值x1²+x2² (x1-3)(x2-3)
4x²-7x-3=0的两个根为:x1,x2,
由韦达定理得:
x1+x2=7/4
x1x2=-3/4
(1)x1²+x2²=(x1+x2)²-2x1x2
=(7/4)²+3/2
=49/16+24/16
=73/16
(2) (x1-3)(x2-3)
=x1x2-3(x1+x2)+9
=-3/4-21/4+9
=-6+9
=3