a=1/2,b=1/3,则(3a^2-ab)/(3a^2+5ab-2b^2)=多少

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a=1/2,b=1/3,则(3a^2-ab)/(3a^2+5ab-2b^2)=多少

a=1/2,b=1/3,则(3a^2-ab)/(3a^2+5ab-2b^2)=多少
a=1/2,b=1/3,则(3a^2-ab)/(3a^2+5ab-2b^2)=多少

a=1/2,b=1/3,则(3a^2-ab)/(3a^2+5ab-2b^2)=多少
(3a^2-ab)/(3a^2+5ab-2b^2)
=a(3a-b)/[(3a-b)(a+2b)]
=a/(a+2b)
=1/2/(1/2+1/3)
=1/2/(5/6)
=3/5

原式=a(3a-b)(3a-b)(a+2b)
=a/(a+2b)
=(1/2)/(1/2+2/3)
=3/7