Toán Lớp 8: cho biểu thức M=x-5/x-4 và N=x+5/2x-x-6/5-x-2x^2-2x-50/2x^2-10x a.tính giá trị M khi x^2-3x=0 b.rút gọn M
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Toán Lớp 8: cho biểu thức M=x-5/x-4 và N=x+5/2x-x-6/5-x-2x^2-2x-50/2x^2-10x a.tính giá trị M khi x^2-3x=0 b.rút gọn M
Comments ( 1 )
Dkxd:x\# 4\\
{x^2} – 3x = 0\\
\Leftrightarrow x = 0/x = 3\\
+ Khi:x = 0 \Leftrightarrow M = \dfrac{{x – 5}}{{x – 4}} = \dfrac{5}{4}\\
+ Khi:x = 3 \Leftrightarrow M = \dfrac{{3 – 5}}{{3 – 4}} = 2\\
b)Dkxd:x\# 0;\# 5\\
N = \dfrac{{x + 5}}{{2x}} – \dfrac{{x – 6}}{{5 – x}} – \dfrac{{2{x^2} – 2x – 50}}{{2{x^2} – 10x}}\\
= \dfrac{{\left( {x + 5} \right)\left( {x – 5} \right) + \left( {x – 6} \right).2x – 2{x^2} + 2x + 50}}{{2x\left( {x – 5} \right)}}\\
= \dfrac{{{x^2} – 25 + 2{x^2} – 12x – 2{x^2} + 2x + 50}}{{2x\left( {x – 5} \right)}}\\
= \dfrac{{{x^2} – 10x + 25}}{{2x\left( {x – 5} \right)}}\\
= \dfrac{{{{\left( {x – 5} \right)}^2}}}{{2x\left( {x – 5} \right)}}\\
= \dfrac{{x – 5}}{{2x}}
\end{array}$