先化简再求值3x[a^2-3x(a-3x)]+a(9x^2-3ax+a),其中x=-1/3,a=-1/2

问题描述:

先化简再求值3x[a^2-3x(a-3x)]+a(9x^2-3ax+a),其中x=-1/3,a=-1/2

3x[a^2-3x(a-3x)]+a(9x^2-3ax+a),=3x(a^2-3ax+9x^2)+a(9x^2-3ax+a),=3a^2x-9ax^2+27x^3+9ax^2-3a^2x+a^2=27x^3+a^2=27*(-1/3)^3+(-1/2)^3=27*(-1/27)-1/8=-1-1/8=-9/8