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\(12.42+12.35+12^2+12\)
\(=12.42+12.35+12.12+12.1\)
\(=12.\left(42+35+12+1\right)\)
\(=12.90\)
\(=1080\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
47.63 = (55 - 8)(55 + 8)
= 55² - 8²
= 3025 - 64
= 2961
--------
47.(63 - 15) - 63.(47 - 15)
= 47.63 - 47.15 - 63.47 + 63.15
= 47.(63 - 63) + 15.(63 - 47)
= 47.0 + 15.16
= 0 + 240
= 240
47.63 = (55 - 8)(55 + 8)
= 55² - 8²
= 3025 - 64
= 2961
--------
47.(63 - 15) - 63.(47 - 15)
= 47.63 - 47.15 - 63.47 + 63.15
= 47.(63 - 63) + 15.(63 - 47)
= 47.0 + 15.16
= 0 + 240
= 240
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\(c.\left[461+\left(-78\right)+40\right]+\left(-461\right)=461-78+40-461=\left(461-461\right)+\left(-78+40\right)=-38.\)
\(d.\left(53-76\right)-\left[-76-\left(-53\right)\right]=53-76+76-53=0.\)
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49 x 36 + 49 x 64
= 49 x (36+64)
= 49 x 100 = 4900
---
g, 218 x 47 + 218 x 52 + 218
= 218 x (47+1+52)
= 218 x 100
= 21800
h, 119 x 27 - 27 x 19
= 27 x (119 - 19)
= 27 x 100
=2700
f: =45(36+64)=45*100=4500
g: =218(47+52+1)
=218*100=21800
h: =27(115-15)=27*100=2700
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Mình dùng phương pháp số 2:
\(5^8=\left(5^2\right)^4=25^4\)
Vì \(15< 25\) nên \(15^4< 25^4\)
Vậy \(15^4< 5^8\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(36\cdot12+12\cdot65-12\)
\(=12\cdot\left(36+65-1\right)\)
\(=12\cdot\left(35+65\right)\)
\(=12\cdot100\)
\(=1200\)
36.12+12.65-12=36.12+12.65-12.1=(36+65-1).12=100.12=1200
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{5}{6}.\frac{8}{7}+\frac{5}{7}.\frac{2}{3}\)
\(=\frac{5}{7}.\frac{8}{6}+\frac{5}{7}.\frac{2}{3}\)
\(=\frac{5}{7}\left(\frac{8}{6}+\frac{2}{3}\right)\)
\(=\frac{5}{7}\left(\frac{8}{6}+\frac{4}{6}\right)\)
\(=\frac{5}{7}.2=\frac{10}{7}\)
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