Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
\(P=\sqrt{\left(\sqrt{2}+\sqrt{5}+\sqrt{7}\right)^2}=\left|\sqrt{2}+\sqrt{5}+\sqrt{7}\right|=\sqrt{2}+\sqrt{5}+\sqrt{7}\)
Ta có
\(P=\sqrt{14+2\sqrt{10}+2\sqrt{14}+2\sqrt{35}}\)
\(\Leftrightarrow P=\sqrt{\left(\sqrt{5}+\sqrt{2}+\sqrt{7}\right)^2}\)
\(\Leftrightarrow P=\sqrt{5}+\sqrt{2}+\sqrt{7}\)
Mà \(P=\sqrt{a}+\sqrt{b}+\sqrt{c}=\sqrt{5}+\sqrt{2}+\sqrt{7}\)
Suy ra \(a+b+c=5+2+7=14\)
\(10+\sqrt{60}-\sqrt{24}-\sqrt{40}\)
\(=10+2\sqrt{15}-2\sqrt{6}-2\sqrt{10}\)
\(=10+2\sqrt{3}.\sqrt{5}-2\sqrt{2}.\sqrt{3}-2\sqrt{2}.\sqrt{5}\)
\(=3+5+2+...\)
\(=\left(\sqrt{3}+\sqrt{5}-\sqrt{2}\right)^2\)
\(\Rightarrow P=-\sqrt{2}+\sqrt{3}+\sqrt{5}\)
\(A=\sqrt{10+\sqrt{24}+\sqrt{40}+\sqrt{60}}\)
\(=\sqrt{10+2\sqrt{6}+2\sqrt{10}+2\sqrt{15}}\)
\(=\sqrt{2+3+5+2\left(\sqrt{2.3}+\sqrt{2.5}+\sqrt{3.5}\right)}\)
\(=\sqrt{\left(\sqrt{2}+\sqrt{3}+\sqrt{5}\right)^2}\)
\(=\sqrt{2}+\sqrt{3}+\sqrt{5}\)
P=\(\sqrt{14+\sqrt{40}+\sqrt{56}+\sqrt{140}}\)=\(\sqrt{2+5+7+2\sqrt{5.2}+2\sqrt{2.7}+2\sqrt{3.5}}\)
=\(\sqrt{\left(\sqrt{2}+\sqrt{5}+\sqrt{7}\right)^2}\)=\(\sqrt{2}+\sqrt{5}+\sqrt{7}\)=\(\sqrt{a}+\sqrt{b}+\sqrt{c}\)
Vậy a+b+c=14
Bài 1:
$14+\sqrt{40}+\sqrt{56}+\sqrt{140}=14+\sqrt{56}+(\sqrt{40}+\sqrt{140})$
=14+2\sqrt{10}+2\sqrt{14}+2\sqrt{35}=(12+2\sqrt{35})+2+(2\sqrt{10}+2\sqrt{14})$
$=(\sqrt{5}+\sqrt{7})^2+2+2\sqrt{2}(\sqrt{5}+\sqrt{7})$
$=(\sqrt{5}+\sqrt{7}+\sqrt{2})^2$
$\Rightarrow \sqrt{14+\sqrt{40}+\sqrt{56}+\sqrt{140}}=\sqrt{2}+\sqrt{5}+\sqrt{7}$
\(\Rightarrow A=\frac{\sqrt{2}+\sqrt{5}+\sqrt{7}}{\sqrt{2}+\sqrt{5}+\sqrt{7}}=1\)
Lời giải:
a) ĐKXĐ: $a,b\geq 0$ và $a,b$ không đồng thời cùng bằng $0$
\(B=\frac{2a+2\sqrt{2}a-2\sqrt{3ab}+2\sqrt{3ab}-3b-2a\sqrt{2}}{a\sqrt{2}+\sqrt{3ab}}=\frac{2a-3b}{\sqrt{a}(\sqrt{2a}+\sqrt{3b})}=\frac{(\sqrt{2a}-\sqrt{3b})(\sqrt{2a}+\sqrt{3b})}{\sqrt{a}(\sqrt{2a}+\sqrt{3b})}\)
\(=\frac{\sqrt{2a}-\sqrt{3b}}{\sqrt{a}}=\sqrt{2}-\sqrt{\frac{3b}{a}}\)
b)
\(a=1+3\sqrt{2}; 3b=30+11\sqrt{8}\Rightarrow \frac{3b}{a}=\frac{30+11\sqrt{8}}{1+3\sqrt{2}}=\frac{(30+11\sqrt{8})(1-3\sqrt{2})}{(1+3\sqrt{2})(1-3\sqrt{2})}\)
\(=\frac{102+68\sqrt{2}}{17}=6+4\sqrt{2}=(2+\sqrt{2})^2\)
\(\Rightarrow \sqrt{\frac{3b}{a}}=2+\sqrt{2}\)
\(\Rightarrow B=\sqrt{2}-(2+\sqrt{2})=-2\)
Bài 1:
a) Để căn thức \(\sqrt{\frac{2}{9-x}}\) có nghĩa thì \(\left\{{}\begin{matrix}\frac{2}{9-x}\ge0\\9-x\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}9-x>0\\x\ne9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x< 9\\x\ne9\end{matrix}\right.\Leftrightarrow x< 9\)
b) Ta có: \(x^2+2x+1\)
\(=\left(x+1\right)^2\)
mà \(\left(x+1\right)^2\ge0\forall x\)
nên \(x^2+2x+1\ge0\forall x\)
Do đó: Căn thức \(\sqrt{x^2+2x+1}\) xác được với mọi x
c) Để căn thức \(\sqrt{x^2-4x}\) có nghĩa thì \(x^2-4x\ge0\)
\(\Leftrightarrow x\left(x-4\right)\ge0\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x\ge0\\x-4\ge0\end{matrix}\right.\\\left\{{}\begin{matrix}x< 0\\x-4< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x\ge0\\x\ge4\end{matrix}\right.\\\left\{{}\begin{matrix}x< 0\\x< 4\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x\ge4\\x< 0\end{matrix}\right.\)
Bài 3:
a) Ta có: \(\sqrt{\left(3-\sqrt{10}\right)^2}\)
\(=\left|3-\sqrt{10}\right|\)
\(=\sqrt{10}-3\)(Vì \(3< \sqrt{10}\))
b) Ta có: \(\sqrt{9-4\sqrt{5}}\)
\(=\sqrt{5-2\cdot\sqrt{5}\cdot2+4}\)
\(=\sqrt{\left(\sqrt{5}-2\right)^2}\)
\(=\left|\sqrt{5}-2\right|\)
\(=\sqrt{5}-2\)(Vì \(\sqrt{5}>2\))
c) Ta có: \(3x-\sqrt{x^2-2x+1}\)
\(=3x-\sqrt{\left(x-1\right)^2}\)
\(=3x-\left|x-1\right|\)
\(=\left[{}\begin{matrix}3x-\left(x-1\right)\left(x\ge1\right)\\3x-\left(1-x\right)\left(x< 1\right)\end{matrix}\right.\)
\(=\left[{}\begin{matrix}3x-x+1\\3x-1+x\end{matrix}\right.=\left[{}\begin{matrix}2x+1\\4x-1\end{matrix}\right.\)
Câu 1:
\(\left\{{}\begin{matrix}\frac{x-1}{x+3}\ge0\\x+3\ne0\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x\ge1\\x< -3\end{matrix}\right.\)
b/
\(\left\{{}\begin{matrix}\frac{x-1}{4-x}\ge0\\4-x\ne0\end{matrix}\right.\) \(\Rightarrow1\le x< 4\)
c/
\(\left\{{}\begin{matrix}\frac{a^3}{b^2}\ge0\\b^2\ne0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a^3\ge0\\b\ne0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a\ge0\\b\ne0\end{matrix}\right.\)
Câu 2:
\(\sqrt{64+6\sqrt{7}}=\sqrt{63+2\sqrt{63}+1}=\sqrt{\left(\sqrt{63}+1\right)^2}=1+\sqrt{63}=1+3\sqrt{7}\)
\(\sqrt{16+8\sqrt{3}}=\sqrt{12+2\sqrt{12.4}+4}=\sqrt{\left(\sqrt{12}+\sqrt{4}\right)^2}=\sqrt{12}+\sqrt{4}=2+2\sqrt{3}\)
\(\sqrt{9-2\sqrt{14}}=\sqrt{7-2\sqrt{7.2}+2}=\sqrt{\left(\sqrt{7}-\sqrt{2}\right)^2}=\sqrt{7}-\sqrt{2}\)
\(13-4\sqrt{3}=\left(2\sqrt{3}\right)^2-2.2\sqrt{2}.1+1^2=\left(2\sqrt{3}-1\right)^2\)
a) \(\left(\sqrt{5}+\sqrt{3}\right)\sqrt{8-2\sqrt{15}}=\left(\sqrt{5}+\sqrt{3}\right)\left(\sqrt{5}-\sqrt{3}\right)=5-3=2\)
câu này \(\sqrt{15}\)đúng hơn \(\sqrt{5}\)
b) \(\sqrt{3-\sqrt{5}}-\sqrt{3+\sqrt{5}}=\frac{\sqrt{6-2\sqrt{5}}-\sqrt{6+2\sqrt{5}}}{\sqrt{2}}=\frac{\sqrt{5}-1-\sqrt{5}-1}{\sqrt{2}}=\frac{-2}{\sqrt{2}}=-\sqrt{2}\)c) \(\sqrt{5-2\sqrt{6}}-\sqrt{5+2\sqrt{6}}=\sqrt{3}-\sqrt{2}-\sqrt{3}-\sqrt{2}=-2\sqrt{2}\)
\(\sqrt{14+\sqrt{40}+\sqrt{56}+\sqrt{140}}\)
\(=\sqrt{2+5+7+2\sqrt{2.5}+2\sqrt{2.7}+2\sqrt{5.7}}\)
\(=\sqrt{\left(\sqrt{2}+\sqrt{5}+\sqrt{7}\right)^2}=\sqrt{2}+\sqrt{5}+\sqrt{7}\)
\(\Rightarrow a+b+c=2+5+7=14\)