Register Now

Login

Lost Password

Lost your password? Please enter your email address. You will receive a link and will create a new password via email.

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

Toán Lớp 8: Tìm x . a ) ( 7 + 2x )² + ( x – 7 )² – 9 = 2( 7 + 2x )( x – 7 ) b ) ( x + 2 )² – x³ + 6x² = 7

Toán Lớp 8: Tìm x .
a ) ( 7 + 2x )² + ( x – 7 )² – 9 = 2( 7 + 2x )( x – 7 )
b ) ( x + 2 )² – x³ + 6x² = 7

Comments ( 1 )

  1. Giải đáp:
    $\begin{array}{l}
    a){\left( {7 + 2x} \right)^2} + {\left( {x – 7} \right)^2} – 9 = 2\left( {7 + 2x} \right)\left( {x – 7} \right)\\
     \Leftrightarrow 49 + 28x + 4{x^2} + {x^2} – 14x + 49 – 9\\
     = 2.\left( {7x – 49 + 2{x^2} – 14x} \right)\\
     \Leftrightarrow 5{x^2} + 14x + 89 = 4{x^2} – 14x – 98\\
     \Leftrightarrow {x^2} + 28x + 187 = 0\\
     \Leftrightarrow {x^2} + 11x + 17x + 187 = 0\\
     \Leftrightarrow \left( {x + 11} \right)\left( {x + 17} \right) = 0\\
     \Leftrightarrow x =  – 11;x =  – 17\\
    Vậy\,x =  – 11;x =  – 17\\
    b){\left( {x + 2} \right)^2} – {x^3} + 6{x^2} = 7\\
     \Leftrightarrow {x^2} + 4x + 4 – {x^3} + 6{x^2} = 7\\
     \Leftrightarrow {x^3} – 7{x^2} – 4x + 3 = 0\\
     \Leftrightarrow \left[ \begin{array}{l}
    x =  – 0,91\\
    x = 0,43\\
    x = 7,48
    \end{array} \right.\\
    Vậy\,x =  – 0,91;x = 0,43;x = 7,48
    \end{array}$

Leave a reply

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

About Melanie