Toán Lớp 8: a) 8x^3 – 50x = 0 b) (x + 3)^2 = 9(2x – 1)^2 c) ????. (???? − 2) − ???? + 2 = 0

Question

Toán Lớp 8:  a) 8x^3 – 50x = 0 b) (x + 3)^2 = 9(2x – 1)^2 c) ????. (???? − 2) − ???? + 2 = 0

buianhtuan · Answer

@ Sun - # bạn b&egrave; l&agrave; tất cả  Gửi bn:  a, 8x&sup3; - 50x = 0 &harr; 2x(4x - 25) = 0 TH1: 2x = 0 &harr; x = 0 : 2 = 0  TH2: 4x - 25 = 0 &harr; 4x = 0 + 25 = 25 &harr; x = 25/4 Vậy gi&aacute; trị xủa x l&agrave; 0 ; 25/4 b, (x + 3)&sup2; = 9(2x - 1)&sup2; &harr; (x + 3)&sup2; - 9(2x - 1)&sup2; = 0 &harr; x&sup2; + 6x + 9 - 9(4x&sup2; - 4x + 1) = 0 &harr; x&sup2; + 6x + 9 - 36x&sup2; + 36x - 9 = 0 &harr; - 35x&sup2; + 52x = 0 &harr; x(52 - 35x) = 0 TH1: x = 0 TH2: 52 - 35x = 0 &harr; 35x = 52 - 0 = 52 &harr; x = 52/35 Vậy gi&aacute; trị của x l&agrave; 0 ; 52/35 c, x(x - 2) - x + 2 = 0 &harr; x(x - 2) - (x - 2) = 0 &harr; (x - 2)(x - 1) = 0 TH1: x - 2 = 0 &harr; x = 0 + 2 = 2 TH2: x - 1 = 0 &harr; x = 0 + 1 =1 Vậy gi&aacute; trị của x l&agrave; 2 ; 1

quynhthanhnghi · Answer

a) 8x^3-50x=0   &hArr;2x(4x^2-25)=0   &hArr;2x(2x-5)(2x+5)=0   &hArr; ( left[  begin{array}{l}2x=0  2x-5=0  2x+5=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=0  x= dfrac{5}{2}  x=- dfrac{5}{2} end{array}  right. )    Vậy S={0,5/2,-5/2}   b) (x+3)^2=9(2x-1)^2   &hArr;(x+3)^2-9(2x-1)=0   &hArr;[x+3-3(2x-1)][x+3+3(2x-1)]=0   &hArr;(x+3-6x+3)(x+3+6x-3)=0   &hArr;7x(-5x+6)=0   &hArr; ( left[  begin{array}{l}-5x+6=0  7x=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x= dfrac{6}{5}  x=0 end{array}  right. )    Vậy S={6/5,0}   c) x(x-2)-x+2=0   &hArr;x(x-2)-(x-2)=0   &hArr;(x-2)(x-1)=0   &hArr; ( left[  begin{array}{l}x-2=0  x-1=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=2  x=1 end{array}  right. )    Vậy S={2,1}