Question

已知X的平方减3乘以X减1等于0,求代数式2乘以X的3次方减3乘以X的平方减11乘以X加8的值

Answer 1

x^2-3x-1=0

x^2-3x=1

2x^3-3x^2-11x+8

=2x^3-6x^2+3x^2-11x+8

=2x(x^2-3x)+3x^2-11x+8

=2x+3x^2-11x+8

=3x^2-9x+8

=3(x^2-3x)+8

=3+8

=11