Cho hình thang ABCD, AB//CD có góc A=góc D= 90 độ, AB=4cm, CD=9cm, BC=13cm. M là trung điểm của AD. Kẻ BK vuông góc với CD tại K.
a) Tứ giác ABKD là hình gì? Tính KC, BK, AD và AM
b) Chứng minh tam giác ABM đồng dạng với tam giác DMC
c) Tính góc BMC
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câu a, \(\dfrac{x}{x+1}\); \(\dfrac{x^2}{1-x}\); \(\dfrac{1}{x^2-1}\) (đk \(x\)≠ -1; 1)
\(x^2\) - 1 = ( \(x\) - 1).(\(x\) + 1)
\(\dfrac{x}{x+1}\) = \(\dfrac{x.\left(x-1\right)}{\left(x+1\right).\left(x-1\right)}\);
\(\dfrac{x^2}{1-x}\) = \(\dfrac{-x^2}{x-1}\)= \(\dfrac{-x^2.\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}\)
\(\dfrac{1}{x^2-1}\) = \(\dfrac{1}{\left(x-1\right)\left(x+1\right)}\)
b, \(\dfrac{10}{x+2}\); \(\dfrac{5}{2x-4}\); \(\dfrac{1}{6-3x}\) (đk \(x\) ≠ -2; 2)
2\(x-4\) = 2.(\(x\) - 2); 6 - 3\(x\) = - 3.(\(x\) - 2)
\(\dfrac{10}{x+2}\) = \(\dfrac{10.2.3\left(x-2\right)}{2.3\left(x+2\right)\left(x-2\right)}\) = \(\dfrac{60\left(x-2\right)}{6\left(x-2\right)\left(x+2\right)}\)
\(\dfrac{5}{2x-4}\) = \(\dfrac{5.3\left(x+2\right)}{2.3\left(x-2\right).\left(x+2\right)}\) = \(\dfrac{15.\left(x+2\right)}{6.\left(x-2\right)\left(x+2\right)}\)
\(\dfrac{1}{6-3x}\) = \(\dfrac{-1}{3.\left(x-2\right)}\) = \(\dfrac{-1.\left(x+2\right)}{3.2.\left(x-2\right)\left(x+2\right)}\) = \(\dfrac{-2.\left(x+2\right)}{6.\left(x-2\right).\left(x+2\right)}\)
c, \(\dfrac{x}{2x-4}\); \(\dfrac{1}{2x+4}\) và \(\dfrac{3}{4-x^2}\) đk \(x\) ≠ 2; -2
\(\dfrac{x}{2x-4}\) = \(\dfrac{x}{2.\left(x-2\right)}\) = \(\dfrac{x.\left(x+2\right)}{2.\left(x-2\right).\left(x+2\right)}\)
\(\dfrac{1}{2x+4}\) = \(\dfrac{1}{2.\left(x+2\right)}\) = \(\dfrac{\left(x-2\right)}{2.\left(x+2\right).\left(x-2\right)}\)
\(\dfrac{3}{4-x^2}\) = \(\dfrac{-3}{\left(x-2\right)\left(x+2\right)}\) = \(\dfrac{-6}{2.\left(x-2\right)\left(x+2\right)}\)
Lời giải:
a. ĐKXĐ: \(\left\{\begin{matrix}
3x\neq 0\\
x+1\neq 0\\
2-4x\neq 0\end{matrix}\right.\Leftrightarrow \left\{\begin{matrix}
x\neq 0\\
x\neq -1\\
x\neq \frac{1}{2}\end{matrix}\right.\)
b.
\(P=\left[\frac{(x+2)(x+1)+3x.2}{3x(x+1)}-3\right].\frac{x+1}{2(1-2x)}-\frac{3x-x^2+1}{3x}\)
\(=\frac{x^2+3x+2+6x-9x(x+1)}{3x(x+1)}.\frac{x+1}{2(1-2x)}-\frac{3x-x^2+1}{3x}\)
\(=\frac{-8x^2+2}{3x(x+1)}.\frac{x+1}{2(1-2x)}-\frac{3x-x^2+1}{3x}\)
\(=\frac{-2(2x-1)(2x+1)(x+1)}{6x(x+1)(1-2x)}-\frac{3x-x^2+1}{3x}=\frac{1+2x}{3x}-\frac{3x-x^2+1}{3x}=\frac{x^2-x}{3x}=\frac{x-1}{3}\)
Tại $x=2023$ thì:
$P=\frac{2023-1}{3}=\frac{2022}{3}=674$
c.
Để $P$ nguyên thì $x-1\vdots 3$
$\Rightarrow x=3k+1$ với $k$ nguyên bất kỳ.
Kết hợp với ĐKXĐ thì $x=3k+1$ với $k\in\mathbb{Z}$
1 How much time do you spend playing video gé on weekends
2 Which family owns the largest field for planting crops in the rural area
1 How much time do you spendplaying video games on weekends?
2 Which family owns the largest field for planting crops in the rural area?
1 I enjoy going to the park for a picnic for it allows me to relax in nature
2 We should go to this village in order to explore traditional ways of life
3 If we throw trash on the ground, the environment gets dirty
1 There are too many cars in some cities, and this causes air pollution
2 She is crazy about taking photographs of beautiful landscapes and scenery
3 The river water is dirty enough to pose threat to aquatic life
1 There are too many cars in some cities, and this causes air pollution.
2 She is crazy about taking photographs of beautiful landscapes and scenery.
3 The river water is dirty enough to pose threat to aquatic life.
1 Avoid touching hot surfaces as they can burn you
2 Are bicycles a popular mode of transport in the countryside
\(B=\dfrac{2x+y}{2x^2-xy}+\dfrac{8y}{y^2-4x^2}+\dfrac{2x-y}{2x^2+xy}\left(x\ne0;y\ne\pm2x\right)\)
\(=\dfrac{2x+y}{x\left(2x-y\right)}-\dfrac{8y}{4x^2-y^2}+\dfrac{2x-y}{x\left(2x+y\right)}\)
\(=\dfrac{\left(2x+y\right)^2}{x\left(2x-y\right)\left(2x+y\right)}-\dfrac{8xy}{x\left(2x-y\right)\left(2x+y\right)}+\dfrac{\left(2x-y\right)^2}{x\left(2x-y\right)\left(2x+y\right)}\)
\(=\dfrac{4x^2+4xy+y^2-8xy+4x^2-4xy+y^2}{x\left(2x-y\right)\left(2x+y\right)}\)
\(=\dfrac{8x^2-8xy+2y^2}{x\left(2x-y\right)\left(2x+y\right)}\)
\(=\dfrac{2\left(4x^2-4xy+y^2\right)}{x\left(2x-y\right)\left(2x+y\right)}\)
\(=\dfrac{2\left(2x-y\right)^2}{x\left(2x-y\right)\left(2x+y\right)}\)
\(=\dfrac{2\left(2x-y\right)}{x\left(2x+y\right)}\)
\(=\dfrac{4x-2y}{2x^2+xy}\)
Với \(x\ne0;y\ne\pm2x\), xét: \(x=\dfrac{1}{2};y=-\dfrac{3}{2}\left(tmdk\right)\)
Thay \(x=\dfrac{1}{2};y=-\dfrac{3}{2}\) vào \(B\), ta được:
\(B=\dfrac{4\cdot\dfrac{1}{2}-2\cdot\dfrac{-3}{2}}{2\cdot\left(\dfrac{1}{2}\right)^2+\dfrac{1}{2}\cdot\dfrac{-3}{2}}=\dfrac{5}{-\dfrac{1}{4}}=-20\)
\(Toru\)