Toán Lớp 8: Bài 1:Tìm x 1) x^3-2x=0 2) x(x-4)+(x-4)=0 3) x(x-3)+4x-12=0 4) 5x(x-2000)-x+2000=0 5) x^3-13x=0 Bài 2: Tính giá trị biểu: b) x(x-1)-y(1

Question

Toán Lớp 8:  Bài 1:Tìm x 1) x^3-2x=0 2) x(x-4)+(x-4)=0 3) x(x-3)+4x-12=0 4) 5x(x-2000)-x+2000=0 5) x^3-13x=0 Bài 2: Tính giá trị biểu: b) x(x-1)-y(1-x) tại x=2001 và y=1999

myngocla · Answer

Bài 1:  b) x(x-4) + (x-4) = 0 => (x-4)(x+1) = 0 => x-4 = 0 hay x+1 = 0 => x    = 4 hay  x     = -1 Vậy x = 4 hay x = -1

lanngocha · Answer

Giải đáp:     $ begin{array}{l} textbf{B&agrave;i 1:}  1.   x^3-2x=0   leftrightarrow x(x^2-2)=0   leftrightarrow  left[ begin{array}{l}x=0  x^2-2=0 end{array} right.   leftrightarrow  left[ begin{array}{l}x=0  x= pm2 end{array} right.  2.   x(x-4)+(x-4)=0   leftrightarrow (x-4)(x+1)=0   leftrightarrow  left[ begin{array}{l}x-4=0  x+1=0 end{array} right.   leftrightarrow  left[ begin{array}{l}x=4  x=-1 end{array} right.  3.   x(x-3)+4x-12=0   leftrightarrow x(x-3)+4(x-3)=0   leftrightarrow (x-3)(x+4)=0   leftrightarrow  left[ begin{array}{l}x-3=0  x+4=0 end{array} right.   leftrightarrow  left[ begin{array}{l}x=3  x=-4 end{array} right.  4.   5x(x-2000)-x+2000=0   leftrightarrow (x-2000)(5x-1)=0   leftrightarrow  left[ begin{array}{l}x=2000  x= dfrac{1}{5} end{array} right.  5.   x^3-13x=0   leftrightarrow x(x^2-13)=0   leftrightarrow  left[ begin{array}{l}x=0  x^2-13=0 end{array} right.   leftrightarrow  left[ begin{array}{l}x=0  x= pm13 end{array} right.   textbf{B&agrave;i 2:}  b.   x(x-1)-y(1-x)  =x(x-1)+y(x-1)  =(x-1)(x+y)   text{Thay}   x=2001, y=1999    text{v&agrave;o biểu thức, ta được:}  (2001-1)(2001+1999)  =2000 times4000  =8000000 end{array}$