帮我看看对不对(3x^2+1/2y-2/3y^2)(-1/2xy)^3=-3/8x^5y^3-1/16x^3 y^4+1/12x^3y^51/7xy^2 . 14(xy)^2 . 1/4x^5=1/2x^8y^4还有一些问题，教教我吧！若2^a=3,2^b=6,2^c=12,求证2b=a=c还有一题若a^2+a+1>2,则(5-a)(6+a)是多少？
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[3x^+(1/2)y-2/3y^][-(1/2)xy]^3=[3x^+(1/2)y-2/3y^][-1/8]x^3y^3=-(3/8)x^5y^3-(1/16)x^3y^4+(1/12)x^3y^5........正确(1/7)xy^2*14(xy)^2*(1/4)x^5=(1/2)x^8y^4...................................正确若2^a=3,2^b=6,2^c=12,求证2b=a+c2^(2b)=(2^b)^=6^=3*12=(2^a)(2^c)=2^(a+c)∴2b=a+c若a^+a+12,则(5-a)(6+a)是多少？(5-a)(6+a)=30-a-a^=31-(a^+a+1)<31-2=29