5/24 - 5/28
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Đặt \(A=\frac{5^{28}+5^{24}+.........+5^4+1}{5^{30}+5^{28}+5^{26}+.....+5^2+1}=\frac{B}{C}\)
Xét tử \(B=5^{28}+5^{24}+........+5^4+1\)
\(\Rightarrow5^4.B=5^{32}+5^{28}+........+5^8+5^4\)
\(\Rightarrow625.B=5^{32}+5^{28}+........+5^8+5^4\)
\(\Rightarrow625.B-B=624.B=5^{32}-1\)
\(\Rightarrow B=\frac{5^{32}-1}{624}\)
Xét mẫu \(C=5^{30}+5^{28}+5^{26}+........+5^2+1\)
\(\Rightarrow5^2.C=5^{32}+5^{30}+5^{28}+.........+5^4+5^2\)
\(\Rightarrow25.C=5^{32}+5^{30}+5^{28}+........+5^4+5^2\)
\(\Rightarrow25.C-C=24.C=5^{32}-1\)
\(\Rightarrow C=\frac{5^{32}-1}{24}\)
\(\Rightarrow A=\frac{B}{C}=\frac{5^{32}-1}{624}:\frac{5^{32}-1}{24}=\frac{5^{32}-1}{624}.\frac{24}{5^{32}-1}=\frac{24}{624}=\frac{1}{26}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
6/11 + 17/28 + 5/11 + 24/60 + 11/28 + 3/5
= ( 6/11 + 5/11 ) + ( 17/28 + 11/28 ) + 24/60 + 3/5
= 1 + 1 + 1
= 3
6/11 + 17/28 + 5/11 + 24/60 + 11/28 + 3/5
= ( 6/11 + 5/11 ) + ( 17/28 + 11/28 ) + 24/60 + 3/5
= 1 + 1 + 1
= 3
![](https://rs.olm.vn/images/avt/0.png?1311)
1) \(35.18-5.7.28\)
\(=35.18-35.28\)
\(=35.\left(18-28\right)\)
\(=35.\left(-10\right)\)
\(=-350\)
2) \(45-5.\left(12+9\right)\)
\(=45-60-45\)
\(=\left(45-45\right)-60\)
\(=0-60\)
\(=-60\)
3) \(24.\left(16-5\right)-16.\left(24-5\right)\)
\(=\left(384-120\right)-\left(384-120\right)\)
\(=264-264\)
\(=0\)
4) \(13.\left(23+22\right)-3.\left(17+28\right)\)
\(=13.45-3.45\)
\(=\left(13-3\right).45\)
\(=10.45\)
\(=450\)
tk ủng hộ nha!!!!!!!!1
1/ 35 . 18 - 5 . 7 . 28
= 35 . 18 - 35 . 28
= 35 . (18 - 28)
= 35 . (-10)
= -350
2/ 45 - 5 . (12 + 9)
= 5 . 9 - 5 . 12 + 5 . 9
= 5 . (9 - 12 + 9)
= 5 . 6
= 30
3/ 24 . (16 - 5) - 16 . (24 - 5)
= 24 . 16 - 24 . 5 - 16 . 24 - 16 . 5
= (24 . 16 - 16 . 24) - (24 . 5 - 16 . 5)
= 0 - [5 . (24 - 16)]
= 0 - [5 . 8]
= 0 - 40
= -40
4/ 13 . (23 + 22) - 3 . (17 + 28)
= 13 . 45 - 3 . 45
= 45 . (13 - 3)
= 45 . 10
= 450
![](https://rs.olm.vn/images/avt/0.png?1311)
Học sinh nhẩm và ghi kết quả như sau:
35 : 5 = 7
28 : 7 = 4
24 : 6 = 4
21 : 3 = 7
35 : 7 = 5
28 : 4 = 7
24 : 4 = 6
21 : 7 = 3
35 : 5 = 7
28 : 7 = 4
24 : 6 = 4
21 : 3 = 7
35 : 7 = 5
28 : 4 = 7
24 : 4 = 6
21 : 7 = 3
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=\dfrac{-3}{5}+\dfrac{28}{5}\cdot\dfrac{9}{14}=\dfrac{-3}{5}+\dfrac{18}{5}=\dfrac{15}{5}=3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
35.18-5.7.28=35.18-35.28=35(18-28)=-350
45-5.12-5.9=45-60-45=-60
=24.16-24.5-16.24-16.5=5(-24-16)=5.-40=-200
35 . 18 - 5 . 7 . 28 = 35 . 18 - 35 . 28
= 35 . (18 - 28)
= 35 . (-10)
= -350
45 - 5 . (12 + 9) = 45 - 5 . 9 + 5 . 12
= 45 - 45 + 60
= 60
24 . (16 - 5) - 16 . (24 - 5) = 24 . 16 - 24 . 5 - 16 . 24 + 16 . 5
= (24 . 16 - 16 . 24) + (16 . 5 - 24 . 5)
=0 + 5 . (16 - 24)
= 5. (-8)
= -40
![](https://rs.olm.vn/images/avt/0.png?1311)
1/ 35. 18 – 5. 7. 28
= 35.(18-28)
=35.-10
=-350
2/ 45 – 5. (12 + 9)
=5.(9-12-9)
=5.-12
=-60
3/ 24. (16 – 5) – 16. (24 - 5)
= 24.16-24.5-16.24+16.5
=-24.5+16.5
=(-24+16).5
=-8.5
=-40
![](https://rs.olm.vn/images/avt/0.png?1311)
5/24 + 5/28 = 140 -120/672 = 20/672 = 5/168