Giải PT:
\(\sqrt{x^2-2x+1}+\sqrt{x^2-4x+4}=\sqrt{1+2014^2+\dfrac{2014^2}{2015^2}}+\dfrac{2014}{2015}\)
Nếu giải không ra thì mong các bạn CTV đăng câu này lên câu hỏi hay giùm nhé.
Giải phương trình: \(\sqrt{2x+1}+\frac{2x-1}{x+3}-\left(2x-1\right)\sqrt{x^2+4}-\sqrt{2}=0\)
Câu này trong đề thi hsg toán 9 tỉnh bắc giang năm 2014-2015. Ai có đáp án cả đề thì cho mk xin nhé . Mk cảm ơn :)))
CÂU 2 :
a, Không dùng máy tính hãy so sánh : \(\dfrac{2014}{\sqrt{2015}}+\dfrac{2015}{\sqrt{2014}}\) và \(\sqrt{2014}+\sqrt{2015}\)
b, Tìm x, y, z biết : \(4x^2+2y^2+2z^2-4xy-2yz+2y-8z+10\le0\)
c, Giair phương trình : \(\sqrt{\dfrac{1}{x+3}}+\sqrt{\dfrac{5}{x+4}}=4\)
a) Ta có: \(\dfrac{2014}{\sqrt{2015}}+\dfrac{2015}{\sqrt{2014}}=\)
\(\dfrac{2015-1}{\sqrt{2015}}+\dfrac{2014+1}{\sqrt{2014}}=\sqrt{2015}-\dfrac{1}{\sqrt{2015}}+\sqrt{2014}+\dfrac{1}{\sqrt{2014}}\)
\(\left(\dfrac{1}{\sqrt{2014}}-\dfrac{1}{\sqrt{2015}}>0\right)\)\(>\sqrt{2014}+\sqrt{2015}\)
Vậy \(\dfrac{2014}{\sqrt{2015}}+\dfrac{2015}{\sqrt{2014}}>\sqrt{2014}+\sqrt{2015}\)
Tính
\(M=\dfrac{1}{2\sqrt{1}+1\sqrt{2}}+\dfrac{1}{3\sqrt{2}+2\sqrt{3}}+.......+\dfrac{1}{2015\sqrt{2014}+2014\sqrt{2015}}\)
Cho M=\(\dfrac{\sqrt{2}-\sqrt{1}}{1+2}+\dfrac{\sqrt{3}-\sqrt{2}}{2+3}+\dfrac{\sqrt{4}-\sqrt{3}}{3+4}+...+\dfrac{\sqrt{2015}-\sqrt{2014}}{2014+2015}\)
Hãy so sánh M với \(\dfrac{1}{2}\)
Chứng tỏ :
\(\dfrac{1}{\sqrt{x+2014}+\sqrt{y+2014}}-\dfrac{1}{\sqrt{2015-x}+\sqrt{2015-y}}+\dfrac{1}{\sqrt{2014-x}+\sqrt{2014-y}}\ne0\)
Tính giá trị biểu thức
\(\dfrac{1}{2\sqrt{1}+1\sqrt{2}}+\dfrac{1}{3\sqrt{2}+2\sqrt{3}}+...+\dfrac{1}{2015\sqrt{2014}+2014\sqrt{2015}}\)
Giải:
\(\dfrac{1}{\left(k+1\right)\sqrt{k}+k\left(\sqrt{k+1}\right)}\) \(=\dfrac{\left(k+1\right)\sqrt{k}-k\left(\sqrt{k+1}\right)}{\left(k+1\right)^2k-k^2\left(k+1\right)}\)
\(=\dfrac{\left(k+1\right)\sqrt{k}-k\left(\sqrt{k+1}\right)}{\left(k+1\right)k\left(k+1-k\right)}=\dfrac{1}{\sqrt{k}}-\dfrac{1}{\sqrt{k+1}}\)
Áp dụng vào biểu thức ta có:
\(\dfrac{1}{2\sqrt{1}+1\sqrt{2}}+\dfrac{1}{3\sqrt{2}+2\sqrt{3}}\) \(+...+\dfrac{1}{2015\sqrt{2014}+2014\sqrt{2015}}\)
\(=\dfrac{1}{\sqrt{1}}-\dfrac{1}{\sqrt{2}}+\dfrac{1}{\sqrt{2}}-\dfrac{1}{\sqrt{3}}+...+\dfrac{1}{\sqrt{2014}}-\dfrac{1}{\sqrt{2015}}\)
\(=1-\dfrac{1}{\sqrt{2015}}\)
Giải hệ phương trình: \(\hept{\begin{cases}2x+\frac{y}{\sqrt{4x^2+1}+2x}+y^2=0\\4\left(\frac{x}{y}\right)^2+2\sqrt{4x^2+1}+y^2=3\end{cases}}\)
Câu này trong đề thi hsg toán 9 tỉnh Thái Bình năm 2014-2015.
Ai có đáp án cả đề thì cho mk xin vs ạ. Mk cảm ơn :))))
Hjhj mình vừa giải trên F
1. Tính
a. \(\left(3\sqrt{2}+2\sqrt{3}\right)\left(2\sqrt{3}-3\sqrt{2}\right)\)
b. \(\dfrac{1}{\sqrt{2013}-\sqrt{2014}}-\dfrac{1}{\sqrt{2014}-\sqrt{2015}}\)
c. \(\sqrt{\left(4+\sqrt{10}\right)^2}-\sqrt{\left(4-\sqrt{10}\right)^2}\)
d. \(\sqrt{3-2\sqrt{2}}+\sqrt{6-4\sqrt{2}}+\sqrt{9-4\sqrt{2}}\)
c: Ta có: \(\sqrt{\left(4+\sqrt{10}\right)^2}-\sqrt{\left(4-\sqrt{10}\right)^2}\)
\(=4+\sqrt{10}-4+\sqrt{10}\)
\(=2\sqrt{10}\)
d: Ta có: \(\sqrt{3-2\sqrt{2}}+\sqrt{6-4\sqrt{2}}+\sqrt{9-4\sqrt{2}}\)
\(=\sqrt{2}-1+2-\sqrt{2}+2\sqrt{2}-1\)
\(=2\sqrt{2}\)
a) \(=\left(2\sqrt{3}\right)^2-\left(3\sqrt{2}\right)^2=12-18=-6\)
b) \(=\dfrac{\sqrt{2013}+\sqrt{2014}}{2013-2014}-\dfrac{\sqrt{2014}+\sqrt{2015}}{2014-2015}=-\sqrt{2013}-\sqrt{2014}+\sqrt{2014}-\sqrt{2015}=-\sqrt{2013}-\sqrt{2015}\)
c) \(=4+\sqrt{10}-4+\sqrt{10}=2\sqrt{10}\)
d) \(=\sqrt{\left(\sqrt{2}-1\right)^2}+\sqrt{\left(2-\sqrt{2}\right)^2}+\sqrt{\left(2\sqrt{2}-1\right)^2}=\sqrt{2}-1+2-\sqrt{2}+2\sqrt{2}-1=2\sqrt{2}\)
1.Tính:
a.\(\sqrt{3-2\sqrt{2}}\) + \(\sqrt{6-4\sqrt{2}}\) +\(\sqrt{9-4\sqrt{2}}\)
b.\(\sqrt{\left(4+\sqrt{10}\right)^2}\) -\(\sqrt{\left(4-\sqrt{10}\right)^2}\)
c.\(\dfrac{1}{\sqrt{2013}-\sqrt{2014}}\) -\(\dfrac{1}{\sqrt{2014}-\sqrt{2015}}\)
2.Giải pt:
a.\(x^2\) -2\(\sqrt{5}x\) +5 =0
b.\(\sqrt{x+3}\) =1
3.Cho:A=\(\dfrac{x-\sqrt{x}}{x+\sqrt{x}+1}\) - \(\dfrac{2x+\sqrt{x}}{\sqrt{x}}\) +\(\dfrac{2\left(x-1\right)}{\sqrt{x}-1}\) ,với x>0 và x\(\ne\) 1
a.Rút gọn A
b.Tìm GTNN của A
1.
a) \(\sqrt{3-2\sqrt{2}}+\sqrt{6-4\sqrt{2}}+\sqrt{9-4\sqrt{2}}=\sqrt{2-2\sqrt{2}+1}+\sqrt{4-2.2.\sqrt{2}+2}+\sqrt{8-2.2\sqrt{2}.1+1}=\sqrt{\left(\sqrt{2}\right)^2-2.\sqrt{2}.1+1^2}+\sqrt{2^2-2.2.\sqrt{2}+\left(\sqrt{2}\right)^2}+\sqrt{\left(2\sqrt{2}\right)^2-2.2\sqrt{2}.1+1^2}=\sqrt{\left(\sqrt{2}-1\right)^2}+\sqrt{\left(2-\sqrt{2}\right)^2}+\sqrt{\left(2\sqrt{2}-1\right)^2}=\left|\sqrt{2}-1\right|+\left|2-\sqrt{2}\right|+\left|2\sqrt{2}-1\right|=\sqrt{2}-1+2-\sqrt{2}+2\sqrt{2}-1=2\sqrt{2}\)
b) \(\sqrt{\left(4+\sqrt{10}\right)^2}-\sqrt{\left(4-\sqrt{10}\right)^2}=\left|4+\sqrt{10}\right|-\left|4-\sqrt{10}\right|=4+\sqrt{10}-4+\sqrt{10}=2\sqrt{10}\)
c) \(\dfrac{1}{\sqrt{2013}-\sqrt{2014}}-\dfrac{1}{\sqrt{2014}-\sqrt{2015}}=\dfrac{\sqrt{2013}+\sqrt{2014}}{\left(\sqrt{2013}-\sqrt{2014}\right)\left(\sqrt{2013}+\sqrt{2014}\right)}-\dfrac{\sqrt{2014}+\sqrt{2015}}{\left(\sqrt{2014}-\sqrt{2015}\right)\left(\sqrt{2014}+\sqrt{2015}\right)}=\dfrac{\sqrt{2013}+\sqrt{2014}}{2013-2014}-\dfrac{\sqrt{2014}+\sqrt{2015}}{2014-2015}=-\left(\sqrt{2013}+\sqrt{2014}\right)+\sqrt{2014}+\sqrt{2015}=-\sqrt{2013}-\sqrt{2014}+\sqrt{2014}+\sqrt{2015}=\sqrt{2015}-\sqrt{2013}\)
2.
a) \(x^2-2\sqrt{5}x+5=0\Leftrightarrow x^2-2.x.\sqrt{5}+\left(\sqrt{5}\right)^2=0\Leftrightarrow\left(x-\sqrt{5}\right)^2=0\Leftrightarrow x-\sqrt{5}=0\Leftrightarrow x=\sqrt{5}\)Vậy S={\(\sqrt{5}\)}
b) ĐK:x\(\ge-3\)
\(\sqrt{x+3}=1\Leftrightarrow\left(\sqrt{x+3}\right)^2=1^2\Leftrightarrow x+3=1\Leftrightarrow x=-2\left(tm\right)\)
Vậy S={-2}
3.
a) \(A=\dfrac{x-\sqrt{x}}{x+\sqrt{x}+1}-\dfrac{2x+\sqrt{x}}{\sqrt{x}}+\dfrac{2\left(x-1\right)}{\sqrt{x}-1}=\dfrac{\sqrt{x}\left(x\sqrt{x}-1\right)}{x+\sqrt{x}+1}-\dfrac{\sqrt{x}\left(2\sqrt{x}+1\right)}{\sqrt{x}}+\dfrac{2\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{\sqrt{x}-1}=\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}{x+\sqrt{x}+1}-\left(2\sqrt{x}+1\right)+2\left(\sqrt{x}+1\right)=\sqrt{x}\left(\sqrt{x}-1\right)-2\sqrt{x}-1+2\sqrt{x}+2=x-\sqrt{x}+1\)
b) Ta có \(A=x-\sqrt{x}+1=x-2\sqrt{x}.\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{3}{4}=\left(\sqrt{x}-\dfrac{1}{2}\right)^2+\dfrac{3}{4}\)
Ta có \(\left(\sqrt{x}-\dfrac{1}{2}\right)^2\ge0\Leftrightarrow\left(\sqrt{x}-\dfrac{1}{2}\right)^2+\dfrac{3}{4}\ge\dfrac{3}{4}\Leftrightarrow A\ge\dfrac{3}{4}\)
Dấu bằng xảy ra khi x=\(\dfrac{1}{4}\)
Vậy GTNN của A=\(\dfrac{3}{4}\)