Toán Lớp 8: Tìm x biết a, 5x(x+5)-x-5=0 b, 3x (2x-7)-(6x+1)(x-15)-2017=0

Question

Toán Lớp 8:  Tìm x biết  a, 5x(x+5)-x-5=0 b, 3x (2x-7)-(6x+1)(x-15)-2017=0

minhtuyethue · Answer

a)5x(x+5)-x-5=0 <=>5x(x+5)-(x+5)=0 <=>(5x-1)(x+5)=0 <=>[(5x-1=0),(x+5=0):} <=>[(5x=1),(x=-5):} <=>$ left[ begin{matrix} x= dfrac{1}{5} x=-5 end{matrix} right.$ Vậy x=1/5 hoặc x=-5 b)3x(2x-7)-(6x+1)(x-15)-2017=0 <=>(6x^2-21x)-(6x^2-90x+x-15)-2017=0 <=>6x^2-21x-(6x^2-89x-15)-2017=0 <=>6x^2-21x-6x^2+89x+15-2017=0 <=>68x-2002=0 <=>68x=2002 <=>x=1001/34 Vậy x=1001/34

quynhmaithu · Answer

Giải đáp:       Lời giải và giải thích chi tiết:   a,  5x(x+5)-x-5=0   &hArr; 5x(x+5)-(x+5)=0   &hArr; (5x-1)(x+5)=0   &hArr;  ( left[  begin{array}{l}5x-1=0  x+5=0 end{array}  right. )    &hArr;  ( left[  begin{array}{l}x= dfrac{1}{5}  x=-5 end{array}  right. )    Vậy S={1/5;-5}   b,3x(2x-7)-(6x+1)(x-15)-2017=0   &hArr; 6x^2-21x-(6x^2-90x+x-15)-2017=0   &hArr; 6x^2-21x-6x^2+89x+15-2017=0   &hArr; 68x=2002   &hArr; x=1001/34   Vậy S={1001/34}