1X²-13X+12=0（x-1)(x-12)=0x=1 x=12所以当X为1或12时,代数式X^2-13X+12的值等于02x^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=423X^2-13X+12=-4X^2+185X^2-13X-...亲 这个题可以用公式法解答么老师还没教十字相乘法1X²-13X+12=0X²-13X+(13/2)^2=(13/2)^2-12(x-13/2)^2=(11/2)^2x=13/2±11/2x=1或x=122x^2-13x+12=42,X^2-13X+(13/2)^2=(13/2)^2+42-12(x-13/2)^2=(17/2)^2x=13/2±17/2x=15或x=-23X^2-13X+12=-4X^2+185X^2-13X=6x^2-13/5x=6/5x^2-13/5x+(13/10)^2=6/5+(13/10)^2(x-13/10)^2=(17/10)^2x=13/10±17/10x=-2/5或x=3