Toán Lớp 7: Giúp mình với X^2-2x X^4-x X^2-1 3x^3-4x

Question

Toán Lớp 7:  Giúp mình với X^2-2x X^4-x X^2-1 3x^3-4x

giangnguyen33 · Answer

a) x^2-2x   &rArr;x^2-2x=0   &rArr;x(x-2)=0   &rArr; ( left[  begin{array}{l}x=0  x-2=0 end{array}  right. )    &rArr; ( left[  begin{array}{l}x=0  x=2 end{array}  right. )    Vậy: x&isin;{0;2}   b) x^4-x   &rArr;x(x^3-1)=0   &rArr; ( left[  begin{array}{l}x=0  x^3-1=0 end{array}  right. )    &rArr; ( left[  begin{array}{l}x=0  x=1 end{array}  right. )    Vậy: x&isin;{0;1}   c) x^2-1   &rArr;x^2-1=0   &rArr;x^2+x-x-1=0   &rArr;x(x+1)-(x+1)=0   &rArr;(x+1)(x-1)=0   &rArr; ( left[  begin{array}{l}x+1=0  x-1=0 end{array}  right. )    &rArr; ( left[  begin{array}{l}x=-1  x=1 end{array}  right. )    Vậy: x&isin;{-1;1}   d) 3x^3-4x   &rArr;x(3x^2-4)=0   &rArr; ( left[  begin{array}{l}x=0  3x^2-4=0 end{array}  right. )    &rArr; ( left[  begin{array}{l}x=0  3x^2=4 end{array}  right. )    &rArr; ( left[  begin{array}{l}x=0  x^2= dfrac{4}{3} end{array}  right. )    &rArr; ( left[  begin{array}{l}x=0  x= sqrt{ dfrac{4}{3}}  x=- sqrt{ dfrac{4}{3}} end{array}  right. )    Vậy: x&isin;{0; sqrt{ frac{4}{3}};- sqrt{ frac{4}{3}}}

maingoctruc · Answer

a) x^2-2x     => x^2 - 2x = 0     => x(x -2) = 0     => x = 0 hoặc x-2 = 0     * x-2 = 0     => x =2     Vậy đa thức c&oacute; 2 nghiệm: x = 0 v&agrave; x= 2      b) x^4-x    => x^4 -x = 0   => x(x^3 - 1) = 0   => x = 0 hoặc x^3 - 1 = 0   * x^3 -1 = 0   => x^3 = 1   => x =1   Vậy đa thức c&oacute; 2 nghiệm: x = 0 v&agrave; x = 1    c) x^2 -1   => x^2 - 1 = 0   => x^2 +x - x -1 = 0   =>x(x+1) - 1(x+1) = 0   => (x-1)(x+1) = 0   => x-1 = 0 hoặc x+1 = 0   => x = 1 hoặc x = -1   Vậy đa thức c&oacute; 2 nghiệm: x = 1; x= -1   d) 3x^3 - 4x   => 3x^3 - 4x = 0   => x(3x^2 - 4) = 0   => x = 0 hoặc 3x^2 - 4 = 0   *3x^2 - 4 = 0   => 3x^2 = 4   => x^2 = 4/3   => x =&plusmn; $ sqrt{ dfrac{4}{3}}$   Vậy đa thức c&oacute; 2 nghiệm: x = 0; x =&plusmn; $ sqrt{ dfrac{4}{3}}$