Toán Lớp 7: 1,tìm x để x-3/x+5<1 2,tìm x để A= x-3/x+5=2x-3/x+1
Leave a reply
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.
Toán Lớp 7: 1,tìm x để x-3/x+5<1 2,tìm x để A= x-3/x+5=2x-3/x+1
Comments ( 1 )
1)DK:x \ne – 5\\
\dfrac{{x – 3}}{{x + 5}} < 1\\
\to \dfrac{{x – 3 – x – 5}}{{x + 5}} < 0\\
\to \dfrac{{ – 8}}{{x + 5}} < 0\\
\to x + 5 > 0\\
\to x > – 5\\
2)DK:x \ne \left\{ { – 5; – 1} \right\}\\
\dfrac{{x – 3}}{{x + 5}} = \dfrac{{2x – 3}}{{x + 1}}\\
\to \left( {x – 3} \right)\left( {x + 1} \right) = \left( {2x – 3} \right)\left( {x + 5} \right)\\
\to {x^2} – 3x + x – 3 = 2{x^2} + 10x – 3x – 15\\
\to {x^2} + 9x – 12 = 0\\
\to \left[ \begin{array}{l}
x = \dfrac{{ – 9 + \sqrt {129} }}{2}\\
x = \dfrac{{ – 9 – \sqrt {129} }}{2}
\end{array} \right.
\end{array}\)