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1/(1.4) + 1/(4.7) + 1/(7.10) + ... + 1/[x.(x + 3)] = 125/376
1/3 . (1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + ... + 1/x - 1/(x + 3) = 125/376
1/3 . [1 - 1/(x + 3)] = 125/376
1 - 1/(x + 3) = 375/376
1/(x + 3) = 1 - 375/376
1/(x + 3) = 1/376
x + 3 = 376
x = 376 - 3
x = 373
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![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a. \(=2\sqrt{3^2}+\sqrt{15}-\sqrt{4.15}=6+\sqrt{15}-2\sqrt{15}=6-\sqrt{15}\)
b. \(=5\sqrt{10}+2\sqrt{5^2}-\sqrt{25.10}=5\sqrt{10}+10-5\sqrt{10}=10\)
c. \(=\left(\sqrt{4.7}-\sqrt{4.3}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}\)
\(=2\sqrt{7^2}-2\sqrt{21}-\sqrt{7^2}+2\sqrt{21}=7\)
d. \(=\left(\sqrt{9.11}-\sqrt{9.2}-\sqrt{11}\right)\sqrt{11}+3\sqrt{22}\)
\(=\left(3\sqrt{11}-3\sqrt{2}-\sqrt{11}\right)\sqrt{11}+3\sqrt{22}\)
\(=3\sqrt{11^2}-3\sqrt{22}-\sqrt{11^2}+3\sqrt{22}=22\)
Bài 3:
a.
\(=\left(1-\sqrt{x}\right)\left(1+\sqrt{x}+\sqrt{x}^2\right)=1-\sqrt{x}^3=1-x\sqrt{x}\)
b.
\(=\left(\sqrt{x}+2\right)\left(\sqrt{x}^2-2\sqrt{x}+2^2\right)=\sqrt{x}^3+2^3=x\sqrt{x}+8\)
c.
\(=\left(\sqrt{x}-\sqrt{y}\right)\left(\sqrt{x}^2+\sqrt{xy}+\sqrt{y}^2\right)=x\sqrt{x}-y\sqrt{y}\)
d.
\(=\left(x+\sqrt{y}\right)\left(x^2-x\sqrt{y}+\sqrt{y}^2\right)=x^3+y\sqrt{y}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1b 2d 3d 4d 5d 1B 2A 3b 4d 5b 6d nhờ ủng hộ
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