Question

1.当x为何值时,代数式x的平方-13x+12的值等于0?

Answer 1

1

X²-13X+12=0

（x-1)(x-12)=0

x=1 x=12

所以当X为1或12时,代数式X^2-13X+12的值等于0

2

x^2-13x+12=42,

x^2-13x-30=0,

(x-15)(x+2)=0,

x1=15,x2=-2

所以当X为15或-2时,代数式X^2-13X+12=42

3

X^2-13X+12=-4X^2+18

5X^2-13X-6=0

(5X+2)(X-3)=0

5X+2=0或X-3=0

X=-2/5或X=3

所以当X为-2/5或3时,代数式X^2-13X+12=-4X^2+18