Toán Lớp 8: a) x³-4x=0 b) x²-4xy+5y²-10y+25=0 Cố đừng làm tắt giúp mình ạa

Question

Toán Lớp 8:  a) x³-4x=0 b) x²-4xy+5y²-10y+25=0 Cố đừng làm tắt giúp mình ạa

maingocquynhnhu2k1 · Answer

Gửi bạn:   $a,$ $x^3-4x=0$   $&rArr;x(x^2-4)=0$   $&rArr;$  ( left[  begin{array}{l}x=0  x^2-4=0 end{array}  right. )    $&rArr;$  ( left[  begin{array}{l}x=0  x^2=4 end{array}  right. )    $&rArr;$  ( left[  begin{array}{l}x=0  x=&plusmn;2 end{array}  right. )    Vậy $x=0$ hoặc $x=&plusmn;2$   $b,$ $x^2-4xy+5y^2-10y+25=0$   $&rArr;x^2-4xy+4y^2+y^2-10y+5^2=0$   $&rArr;(x-2y)^2+(y-5)^2=0$   $&rArr;$  ( left[  begin{array}{l}x-2y=0  y-5 end{array}  right. )    $&rArr;$  ( left[  begin{array}{l}x=2y  y=5 end{array}  right. )    $&rArr;$  ( left[  begin{array}{l}x=10  y=5 end{array}  right. )    Vậy $x=10$ v&agrave; $y=5$

lanhuongthu · Answer

#andy                     [ begin{array}{l} a){x^3} - 4x = 0     Leftrightarrow x({x^2} - 4) = 0     Leftrightarrow x left( {x - 2}  right) left( {x + 2}  right) = 0     Leftrightarrow  left[  begin{array}{l} x = 0   x - 2 = 0   x + 2 = 0  end{array}  right.  Leftrightarrow  left[  begin{array}{l} x = 0   x = 2   x =  - 2  end{array}  right.     Rightarrow S  in  left { {0;2; - 2}  right }   b){x^2} - 4xy + 5{y^2} - 10y + 25 = 0     Leftrightarrow {x^2} - 4xy + 4{y^2} + {y^2} - 10y + {5^2} = 0     Leftrightarrow {(x - 2y)^2} + {(y - 5)^2} = 0     Leftrightarrow  left[  begin{array}{l} x - 2y = 0   y - 5  end{array}  right.     Leftrightarrow  left[  begin{array}{l} x = 2y   x = 5  end{array}  right.     Leftrightarrow  left[  begin{array}{l} x = 15   y = 5  end{array}  right.  end{array} ]