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NT
3
29 tháng 8 2019
a) = a^10 - a + a^5 - a^2 + a^2 + a + 1
= a(a^9 - 1) + a^2(a^3 - 1) + (a^2 + a + 1)
= a.(a^3-1)(a^6 + a^3 + 1) + a^2(a-1)(a^2+a+1) + (a^2 + a + 1)
= a.(a-1)(a^2 + a + 1)(a^6 + a^3 + 1) + a^2(a-1)(a^2+a+1) + (a^2 + a + 1)
= (a^2 + a + 1)[(a.(a-1)(a^6 + a^3 + 1) + a^2 + 1]
b) x^5 - x^4 - 1 = x^5 - x^4 + x^3 - x^3 + x^2 - x - x^2 + x - 1
= x^3(x^2 - x + 1) - x(x^2 - x + 1) - (x^2 - x + 1)
= (x^2 - x + 1)(x^3 - x - 1)
2T
29 tháng 8 2019
a) \(a^{10}+a^5+1\)
\(=\left(a^{10}-a^9+a^7-a^6+a^5-a^3+a^2\right)\)
\(+\left(a^9-a^8+a^6-a^5+a^4-a^2+a\right)\)
\(+\left(a^8-a^7+a^5-a^4+a^3-a+1\right)\)
\(=a^2\left(a^8-a^7+a^5-a^4+a^3-a+1\right)\)
\(+a\left(a^8-a^7+a^5-a^4+a^3-a+1\right)\)
\(+\left(a^8-a^7+a^5-a^4+a^3-a+1\right)\)
\(=\left(a^2+a+1\right)\left(a^8-a^7+a^5-a^4+a^3-a+1\right)\)
21 tháng 8 2022
a: Đặt \(x^2-4=a\)
Pt sẽ là \(a=3\sqrt{xa}\)
\(\Rightarrow a^2=9xa\)
\(\Leftrightarrow a\left(a-9x\right)=0\)
\(\Leftrightarrow\left(x^2-4\right)\left(x^2-4-9x\right)=0\)
hay \(x\in\left\{2;-2;\dfrac{9+\sqrt{97}}{2};\dfrac{9-\sqrt{97}}{2}\right\}\)
d: Đặt \(\sqrt{x^2-x+1}=a;\sqrt{x^2+x+1}=b\)
Pt sẽ là 2a+b=ab+2
=>(b-2)(1-a)=0
=>b=2 và 1-a
\(\Leftrightarrow\left\{{}\begin{matrix}x^2+x+1=4\\x^2-x+1=1\end{matrix}\right.\Leftrightarrow x\in\varnothing\)
AH
Akai Haruma
Giáo viên
26 tháng 6 2019
Bài 1:
\(A=\sqrt{5-2\sqrt{6}}+\sqrt{5+2\sqrt{6}}=\sqrt{2+3-2\sqrt{2.3}}+\sqrt{2+3+2\sqrt{2.3}}\)
\(=\sqrt{(\sqrt{2}-\sqrt{3})^2}+\sqrt{\sqrt{2}+\sqrt{3})^2}\)
\(=|\sqrt{2}-\sqrt{3}|+|\sqrt{2}+\sqrt{3}|=\sqrt{3}-\sqrt{2}+\sqrt{2}+\sqrt{3}=2\sqrt{3}\)
\(B=(\sqrt{10}+\sqrt{6})\sqrt{8-2\sqrt{15}}\)
\(=(\sqrt{10}+\sqrt{6}).\sqrt{3+5-2\sqrt{3.5}}\)
\(=(\sqrt{10}+\sqrt{6})\sqrt{(\sqrt{5}-\sqrt{3})^2}\)
\(=\sqrt{2}(\sqrt{5}+\sqrt{3})(\sqrt{5}-\sqrt{3})=\sqrt{2}(5-3)=2\sqrt{2}\)
\(C=\sqrt{4+\sqrt{7}}+\sqrt{4-\sqrt{7}}\)
\(C^2=8+2\sqrt{(4+\sqrt{7})(4-\sqrt{7})}=8+2\sqrt{4^2-7}=8+2.3=14\)
\(\Rightarrow C=\sqrt{14}\)
\(D=(3+\sqrt{5})(\sqrt{5}-1).\sqrt{2}\sqrt{3-\sqrt{5}}\)
\(=(3+\sqrt{5})(\sqrt{5}-1).\sqrt{6-2\sqrt{5}}\)
\(=(3+\sqrt{5})(\sqrt{5}-1).\sqrt{5+1-2\sqrt{5.1}}\)
\(=(3+\sqrt{5})(\sqrt{5}-1).\sqrt{(\sqrt{5}-1)^2}\)
\(=(3+\sqrt{5})(\sqrt{5}-1)^2=(3+\sqrt{5})(6-2\sqrt{5})=2(3+\sqrt{5})(3-\sqrt{5})=2(3^2-5)=8\)
AH
Akai Haruma
Giáo viên
26 tháng 6 2019
Bài 2:
a) Bạn xem lại đề.
b) \(x-2\sqrt{xy}+y=(\sqrt{x})^2-2\sqrt{x}.\sqrt{y}+(\sqrt{y})^2=(\sqrt{x}-\sqrt{y})^2\)
c)
\(\sqrt{xy}+2\sqrt{x}-3\sqrt{y}-6=(\sqrt{x}.\sqrt{y}+2\sqrt{x})-(3\sqrt{y}+6)\)
\(=\sqrt{x}(\sqrt{y}+2)-3(\sqrt{y}+2)=(\sqrt{x}-3)(\sqrt{y}+2)\)
28 tháng 5 2019
Bài 1 :
a)\(\sqrt{-2\text{x}+3}\) <=> -2x+3 \(\ge\)0 <=> -2x \(\ge\) -3 <=> x\(\le\) \(\frac{3}{2}\)
b)\(\sqrt{\frac{4}{x+3}}< =>x+3>0< =>x>-3\)
Bài 2 :
a)\(\sqrt{\left(4+\sqrt{2}\right)^2}=\left|4+\sqrt{2}\right|=4+\sqrt{2}\)
b)\(2\sqrt{3}+\sqrt{\left(2-\sqrt{3}\right)^2}=2\sqrt{3}+\left|2-\sqrt{3}\right|=2\sqrt{3}+2-\sqrt{3}=2+\sqrt{3}\)
c) \(\sqrt{\left(3-\sqrt{3}\right)^2}=\left|3-\sqrt{3}\right|=3-\sqrt{3}\)
Bài 3 :
a) \(\sqrt{9-4\sqrt{5}}-\sqrt{5}=-2\)
VT = \(\sqrt{5-2.2.\sqrt{5}+2^2}-\sqrt{5}\)
=\(\sqrt{\left(\sqrt{5}\right)^2-4\sqrt{5}+2^2}-\sqrt{5}\)
=\(\sqrt{\left(\sqrt{5}-2\right)^2}-\sqrt{5}\)
=|\(\sqrt{5-2}\)| -\(\sqrt{5}\)
= \(\sqrt{5}-2-\sqrt{5}\)
= -2 = VP
b)\(\sqrt{23+8\sqrt{7}}-\sqrt{7}=4\)
VT = \(\sqrt{7+2.4.\sqrt{7}+4^2}-\sqrt{7}\)
= \(\sqrt{\left(\sqrt{7}+4\right)^2}-\sqrt{7}\)
= |\(\sqrt{7}+4\)| -\(\sqrt{7}\)
=\(\sqrt{7}+4-\sqrt{7}\)
= 4 =VP
c) \(\left(4-\sqrt{7}\right)^2=23-8\sqrt{7}\)
VT = \(16-8\sqrt{7}+7\)
= 23 - \(8\sqrt{7}\) = VP
Bài 4:
a)\(\frac{x^2-5}{x+\sqrt{5}}=\frac{x^2-\left(\sqrt{5}\right)^2}{x+\sqrt{5}}=\frac{\left(x+\sqrt{5}\right)\left(x-\sqrt{5}\right)}{x+\sqrt{5}}=x-\sqrt{5}\)
Tương tự
Bài 5 :
a) \(\sqrt{x^2+6\text{x}+9}=3\text{x}-1\)
=> \(\sqrt{\left(x+3^2\right)}\) = 3x-1
=> x+3 = 3x-1
+) x+3 =3x-1 => x= 2
+)x+3=-3x-1 => x= \(\frac{-1}{2}\) ( không tmđk)
b)+c) Tương tự
18 tháng 7 2020
a) Ta có: \(3\sqrt{2}+4\sqrt{8}-\sqrt{18}\)
\(=\sqrt{2}\left(3+4\cdot2-3\right)\)
\(=8\sqrt{2}\)
b) Ta có: \(\sqrt{3}-\frac{1}{3}\sqrt{27}+2\sqrt{507}\)
\(=\sqrt{3}\left(1-\frac{1}{3}\cdot\sqrt{9}+2\cdot\sqrt{169}\right)\)
\(=\sqrt{3}\left(1-1+26\right)\)
\(=26\sqrt{3}\)
c) Ta có: \(\sqrt{25a}+\sqrt{49a}-\sqrt{64a}\)
\(=\sqrt{25}\cdot\sqrt{a}+\sqrt{49}\cdot\sqrt{a}-\sqrt{64}\cdot\sqrt{a}\)
\(=\sqrt{a}\left(5+7-8\right)\)
\(=4\sqrt{a}\)
d) Ta có: \(-\sqrt{36b}-\frac{1}{3}\sqrt{54b}+\frac{1}{5}\sqrt{150b}\)
\(=-\sqrt{6b}\cdot\sqrt{6}-\frac{1}{3}\cdot\sqrt{6b}\cdot\sqrt{9}+\frac{1}{5}\cdot\sqrt{6b}\cdot\sqrt{25}\)
\(=-\sqrt{6b}\left(\sqrt{6}+1-1\right)\)
\(=-\sqrt{6b}\cdot\sqrt{6}=-6\sqrt{b}\)
NV
Nguyễn Việt Lâm
Giáo viên
19 tháng 4 2020
Câu 3: đề là \(\sqrt{x+5}-\sqrt{x-2}\) hay \(\sqrt{x+5}-\sqrt{x+2}\)?
Câu 4:
ĐKXĐ: \(x\le9\)
Đặt \(\left\{{}\begin{matrix}\sqrt[3]{x-4}=a\\\sqrt{9-x}=b\end{matrix}\right.\) ta có hệ:
\(\left\{{}\begin{matrix}a-b=-1\\a^3+b^2=5\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}b=a+1\\a^3+b^2=5\end{matrix}\right.\)
\(\Rightarrow a^3+\left(a+1\right)^2=5\)
\(\Leftrightarrow a^3+a^2+2a-4=0\) \(\Rightarrow a=1\)
\(\Rightarrow\sqrt[3]{x-4}=1\Rightarrow x-4=1\Rightarrow x=5\)
5.
ĐKXĐ: \(x\ge-\frac{17}{16}\)
\(\Leftrightarrow8x^2-15x-23-\left(x+1\right)\sqrt{16x+17}=0\)
\(\Leftrightarrow\left(x+1\right)\left(8x-23\right)-\left(x+1\right)\sqrt{16x+17}=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\8x-23=\sqrt{16x+17}\left(1\right)\end{matrix}\right.\)
\(\left(1\right)\Leftrightarrow16x+17-2\sqrt{16x+17}-63=0\)
Đặt \(\sqrt{16x+17}=t\ge0\)
\(\Rightarrow t^2-2t-63=0\Rightarrow\left[{}\begin{matrix}t=9\\t=-7\left(l\right)\end{matrix}\right.\)
\(\Rightarrow\sqrt{16x+17}=9\Leftrightarrow x=\frac{32}{3}\)
PA
31 tháng 7 2017
\(\sqrt{x\left(x-2\right)}+\sqrt{x\left(x-5\right)}=\sqrt{x\left(x+3\right)}\)
\(\Leftrightarrow\sqrt{x}\left(\sqrt{x-2}+\sqrt{x-5}-\sqrt{x+3}\right)=0\)
TH1: x = 0 (nhận)
TH2:
\(\sqrt{x-2}+\sqrt{x-5}-\sqrt{x+3}=0\)
\(\Leftrightarrow\left(\sqrt{x-2}-2\right)+\left(\sqrt{x-5}-1\right)-\left(\sqrt{x+3}-3\right)=0\)
\(\Leftrightarrow\frac{x-2-4}{\sqrt{x-2}+2}+\frac{x-5-1}{\sqrt{x-5}+1}-\frac{x+3-9}{\sqrt{x+3}+3}=0\)
\(\Leftrightarrow\left(\frac{1}{\sqrt{x-2}+2}+\frac{1}{\sqrt{x-5}+1}-\frac{1}{\sqrt{x+3}+3}\right)\left(x-6\right)=0\)
Pt \(\frac{1}{\sqrt{x-2}+2}+\frac{1}{\sqrt{x-5}+1}-\frac{1}{\sqrt{x+3}+3}=0\) vô no
=> x - 6 = 0
<=> x = 6 (nhận)
\(a,x^8+14x^4+1=\left(x^8+14x^4+49\right)-48\)
\(=\left(x^4+7\right)^2-48\)
\(=\left(x^4+7+\sqrt{48}\right)\left(x^4+7-\sqrt{48}\right)\)
\(b,x^8+98x^4+1\)
\(=\left(x^8+98x^4+2401\right)-2400\)
\(=\left(x^4+49\right)^2-2400\)
\(=\left(x^4+49+20\sqrt{6}\right)\left(x^4+49-20\sqrt{6}\right)\)
Mình nghĩ vậy k bt đúng k :)