Toán Lớp 8: tìm x 3x(12x-4)-(6x-3)^2=30 2x(5-2x)+2x(x-1)=15-2(1+x)(x-1) 3(2x-1)-5(x-3)=24-15x 2x^2+3(x-1)^2=5x(x+1) ai làm nhanh em cho trlhn ạ

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Toán Lớp 8:  tìm x 3x(12x-4)-(6x-3)^2=30 2x(5-2x)+2x(x-1)=15-2(1+x)(x-1) 3(2x-1)-5(x-3)=24-15x 2x^2+3(x-1)^2=5x(x+1) ai làm nhanh em cho trlhn ạ

thanhthuythu · Answer

Lời giải:     1)   3x(12x-4)-(6x-3)^2=30   &hArr;36x^(2)-12x-[(6x)^(2)-2.6x.3+3^2]=30   &hArr;36x^(2)-12x-36x^(2)+36x-9-30=0   &hArr;(36x^(2)-36x^2)+(-12x+36x)+(-9-30)=0   &hArr;24x-39=0   &hArr;24x=39   &hArr;x=39/24=13/8   Vậy x=13/8   2)   2x(5-2x)+2x(x-1)=15-2(1+x)(x-1)   &hArr;10x-4x^(2)+2x^(2)-2x=15-2(x^(2)-1)   &hArr;-2x^(2)+8x-15+2x^(2)-2=0   &hArr;8x-17=0   &hArr;8x=17   &hArr;x=17/8   Vậy x=17/8   3)   3(2x-1)-5(x-3)=24-15x   &hArr;6x-3-5x+15=24-15x   &hArr;x+15x=24-12   &hArr;16x=12   &hArr;x=12/16=3/4   Vậy x=3/4   4)   2x^(2)+3(x-1)^2=5x(x+1)   &hArr;2x^(2)+3(x^(2)-2x+1)=5x^(2)+5x   &hArr;5x^(2)-6x+3-5x^(2)-5x=0   &hArr;-11x=-3   &hArr;x=3/11   Vậy x=3/11

behocgioitoan · Answer

Giải đáp:   a/ 3x(12x-4)-(6x-3)&sup2;=30     &hArr;36x&sup2;-12x-36x&sup2;+36x-9=30     &hArr;(36x&sup2;-36x&sup2;)+(36x-12x)-(9+30)=0     &hArr;24x-39=0     &hArr;24x=39     &hArr;x=$ frac{39}{24}$      &hArr;x=$ frac{13}{8}$         b/ 2x(5-2x)+2x(x-1)=15-2(1+x)(x-1)     &hArr;2x(5-2x+x-1)=15-2(x&sup2;-1)     &hArr;2x(5-x-1)=15-2(x&sup2;-1)     &hArr;10x-2x&sup2;-2x=15-2x&sup2;+2     &hArr;10x-2x&sup2;-2x-15+2x&sup2;-2=0     &hArr;(10x-2x)+(2x&sup2;-2x&sup2;)+(-2-15)=0     &hArr;8x-17=0     &hArr;8x=17     &hArr;x=$ frac{17}{8}$         c/3(2x-1)-5(x-3)=24-15x     &hArr;6x-3-5x+15=24-15x     &hArr;x+12=24-15x     &hArr;x+15x=24-12     &hArr;16x=12     &hArr;x=$ frac{16}{12}$      &hArr;x=$ frac{4}{3}$         d/2x&sup2;+3(x-1)&sup2;=5x(x+1)     &hArr;2x&sup2;+3(x&sup2;-2x+1)=5x(x+1)     &hArr;2x&sup2;+3x&sup2;-6x+3=5x&sup2;+5     &hArr;5x&sup2;-6x+3=5x&sup2;+5     &hArr;5x&sup2;-6x-5x&sup2;=5-3     &hArr;-6x=2     &hArr;x=$ frac{-2}{6}$      &hArr;x=$ frac{-1}{3}$