a=1/2,b=1/3,则(3a^2-ab)/(3 - 知识问答

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

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(3a²-ab)/(3a²+5ab-2b²)
十字相乘法对分母因式分解
3a -b
a 2b
=a(3a-b)/[(3a-b)(a+2b)]
=a/(a+2b)
=(1/2)/(1/2+2/3)
=(1/2)/(7/6)
=3/7
不懂请问

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