初中分式的加减 3/a^2-4a-5-4/a^-2a-15(3/a^2-4a-5)-(4/a^-2a-15)

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初中分式的加减 3/a^2-4a-5-4/a^-2a-15(3/a^2-4a-5)-(4/a^-2a-15)

初中分式的加减 3/a^2-4a-5-4/a^-2a-15(3/a^2-4a-5)-(4/a^-2a-15)
初中分式的加减 3/a^2-4a-5-4/a^-2a-15
(3/a^2-4a-5)-(4/a^-2a-15)

初中分式的加减 3/a^2-4a-5-4/a^-2a-15(3/a^2-4a-5)-(4/a^-2a-15)
(3/a^2-4a-5)-(4/a^-2a-15)
=3/(a-5)(a+1)-4/(a-5)(a+3)
=[3(a+3)-4(a+1)]/(a+1)(a+3)(a-5)
=(3a+9-4a-4)/(a+1)(a+3)(a-5)
=-(a-5)/(a+1)(a+3)(a-5)
=-1/(a+1)(a+3)

(3/a^2-4a-5)-(4/a^-2a-15)
=3/a^2-4a-5-4/a^+2a+15
=(3/a^2-4/a^2)-(4a-2a)-(5-15)
=-1/a^2-2a+10