Question

若代数式x-x²+2的值等于5,则代数式3x²-3x+7的值是多少

Answer 1

x-x²+2=5

则

x-x²=3

x^2-x=-3

3x²-3x+7

=3(x^2-x)+7

=3*(-3)+7

=-9+7

= -2