Toán Lớp 8: Tìm x a). 3x(x-5)-4x+20=0 b). 2-49x=0 c). (2x+3)(x-5)-(x+2)(2x-5)=32

Question

Toán Lớp 8:  Tìm x a).    3x(x-5)-4x+20=0 b).    2-49x=0 c).    (2x+3)(x-5)-(x+2)(2x-5)=32

huenthanh97 · Answer

Giải đáp+Lời giải và giải thích chi tiết:      a) 3x.(x-5)-4x+20=0     &hArr; 3x.(x-5)-4.(x-5)=0     &hArr; (3x-4).(x-5)=0     &hArr; 3x-4=0      &hArr; 3x=4      &hArr; x=4/3     &hArr; x-5=0        &hArr; x=5        &hArr; x=5     Vậy x &isin; {4/3;5}     b) 2-49x=0     &hArr; -49x=-2     &hArr; x=2/49     Vậy x=2/49     c) (2x+3).(x-5)-(x+2).(2x-5)=32     &hArr; (2x&sup2;-10x+3x-15)-(2x&sup2;-5x+4x-10)=32     &hArr; 2x&sup2;-7x-15-2x&sup2;+x+10=32     &hArr; (2x&sup2;-2x&sup2;)+(x-7x)+(10-15)=32     &hArr; -6x-5=32     &hArr; -6x=37     &hArr; x=-37/6     Vậy x=-37/6     @Festivals

buianhtuan · Answer

a) 3x(x-5)-4x+20=0   &hArr;3x(x-5)-4(x-5)=0   &hArr;(x-5)(3x-4)=0   &hArr; ( left[  begin{array}{l}x-5=0  3x-4=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=5  x= dfrac{4}{3} end{array}  right. )    Vậy x=5 hoặc x=4/3   b) 2-49x=0   &hArr;-49x=-2   &hArr;x=2/(49)   Vậy x=2/(49)   c) (2x+3)(x-5)-(x+2)(2x-5)=32   &hArr;2x^2-10x+3x-15-2x^2+5x-4x+10=32   &hArr;-6x-5=32   &hArr;-6x=37   &hArr;x=-(37)/6   Vậy x=-(37)/6