设m,n为实数,若将运算符号"*"定义为m*n=m^2-n^2+2m+3n,问x为何值时,式子x*x-3的值为17.

x*x-3=17

x^2-x^2+2x+3x-3=17

5x=20

x=4

x=4时,x*x-3的值为17.

4,你代进入看看肯定对啦

x*x-3=x^2-x^2+2x+3x-3=5x-3
5x-3=17
5x=20
x=4

m*n=m^2-n^2+2m+3n,
所以x*(x-3)
=x^2-(x-3)^2+2x+3(x-3)=17
x^2-x^2+6x-9+2x+3x-9=17
11x=35
x=35/11

根据定义可得x*x=5x,原式=5x-3=17，x=4