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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: Tìm x,y,z a, x ² + 3y ² +2z ² – 2x +12y + 4z + 15 = 0 b,x ² + y ² + 2z ² + 4x – 4y -6z -2xz +9 = 0

Toán Lớp 8: Tìm x,y,z
a, x ² + 3y ² +2z ² – 2x +12y + 4z + 15 = 0
b,x ² + y ² + 2z ² + 4x – 4y -6z -2xz +9 = 0

Comments ( 1 )

  1. Giải đáp:
    $a)  \left\{\begin{array}{l} x=1\\y=-2\\z=-1\end{array} \right..$
    Lời giải và giải thích chi tiết:
    $a)x^2+ 3y^2 +2z^2 – 2x +12y + 4z + 15 = 0\\ \Leftrightarrow x^2 – 2x+1+ 3y^2+12y +12+2z^2  + 4z + 2 = 0\\ \Leftrightarrow (x-1)^2+ 3(y^2+4y +4)+2(z^2  + 2z + 1) = 0\\ \Leftrightarrow (x-1)^2+ 3(y+2)^2+2(z+1)^2 = 0\\ \text{Do }(x-1)^2 \ge 0 \ \forall \ x; 3(y+2)^2 \ge 0 \ \forall \ y; 2(z+1)^2 \ge 0 \ \forall \ z\\ \Rightarrow (x-1)^2+ 3(y+2)^2+2(z+1)^2 = 0\\ \Leftrightarrow  \left\{\begin{array}{l} x-1=0\\y+2=0\\z+1= 0\end{array} \right.\\ \Leftrightarrow  \left\{\begin{array}{l} x=1\\y=-2\\z=-1\end{array} \right..$

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222-9+11+12:2*14+14 = ? ( )

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