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0.54x1等于4.24解方程

x1^2+x1-7=0,得到:x1^2=7-x1,同理x2^2=7-x2. x1^3-8x2^2+54 =x1*x1^2-8(7-x2)+54 =x1*(7-x1)-56+8x2+54 =7x1-x1^2+8x2-2 =7x1-(7-x1)+8x2-2 =7x1-7+x1+8x2-2 =8x1+8x2-9 =8(x1+x2)-9 =8*(-1)-9 x1+x2=-1,由韦达定理得到。 =-17.

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