Toán Lớp 8: Tìm x biết: a.x ³-9x=0 b.2x(x+2)-2x-4=0 c.x ²+25=10x d.x ²-5x+4=0

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Toán Lớp 8:  Tìm x biết: a.x ³-9x=0 b.2x(x+2)-2x-4=0 c.x ²+25=10x d.x ²-5x+4=0

dananhthumai · Answer

Lời giải và giải thích chi tiết:   a) $x^3-9x=0$   $&hArr;x(x^2-9)=0$   $&hArr;x(x-3)(x+3)=0$   $&hArr; left[  begin{array}{l}x=0  x-3=0  x+3=0 end{array}  right.&hArr; left[  begin{array}{l}x=0  x=3  x=-3 end{array}  right.$   V&acirc;̣y $S= {-3;0;3 }$   b) $2x(x+2)-2x-4=0$   $&hArr;2x(x+2)-2(x+2)=0$   $&hArr;2(x-1)(x+2)=0$   $&hArr; left[  begin{array}{l}x-1=0  x+2=0 end{array}  right.&hArr; left[  begin{array}{l}x=1  x=-2 end{array}  right.$   V&acirc;̣y $S= {-2;1 }$   c) $x^2+25=10x$   $&hArr;x^2-10x+25=0$   $&hArr;(x-5)^2=0$   $&hArr;x-5=0$   $&hArr;x=5$   V&acirc;̣y $S= {5 }$   d) $x^2-5x+4=0$   $&hArr;x^2-x-4x+4=0$   $&hArr;x(x-1)-4(x-1=0)$   $&hArr;(x-1)(x-4)=0$   $&hArr; left[  begin{array}{l}x-1=0  x-4=0 end{array}  right.&hArr; left[  begin{array}{l}x=1  x=4 end{array}  right.$   V&acirc;̣y $S= {1;4 }$.

minhtamnguyet88 · Answer

Giải đáp+Lời giải và giải thích chi tiết:   a)   $x^3-9x=0$   &hArr;$x(x^2-9)=0$   &hArr;$x(x-3)(x+3)=0$   &hArr; ( left[  begin{array}{l}x=0  x-3=0  x+3=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=0  x=3  x=-3 end{array}  right. )    Vậy S={0,3,-3}   b)   $2x(x+2)-2x-4=0$   &hArr;$2x(x+2)-(2x+4)=0$   &hArr;$2x(x+2)-2(x+2)=0$   &hArr;$2(x+2)(x-1)=0$   &hArr; ( left[  begin{array}{l}x+2=0  x-1=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=-2  x=1 end{array}  right. )    Vậy S={2,-1}   c)   $x^2+25=10x$   &hArr;$x^2-10x+25=0$   &hArr;$x^2-2.5.x+5^2=0$   &hArr;$(x-5)^2=0$   &hArr;$x-5=0$   &hArr;$x=5$   Vậy S={5}   d)   $x^2-5x+4=0$   &hArr;$(x^2-x)-(4x-4)=0$   &hArr;$x(x-1)-4(x-1)=0$   &hArr;$(x-1)(x-4)=0$   &hArr; ( left[  begin{array}{l}x-1=0  x-4=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=1  x=4 end{array}  right. )    Vậy S={1,4}