y-9+21=43+39
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= 39 . (53 + 43) - 21 . (53 + 47)
= 39 . 96 - 21 . 100
= 3744 - 2100
= 1644
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a) 21: 25 =\(\dfrac{21}{25}\)
30: 43 = \(\dfrac{30}{43}\)
61: 69 = \(\dfrac{61}{69}\)
17: 100 = \(\dfrac{17}{100}\)
b)9 : 4 = \(\dfrac{9}{4}\)
51: 7 = \(\dfrac{51}{7}\)
60 : 39 = \(\dfrac{60}{39}\)
200 : 163 = \(\dfrac{200}{163}\)
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a) 166.(-127)+166.234+(-234).166-234.127
166.(-234+234)+127.(-166-234)
=0+127.(-400)
=-50800
b) 53.39+43.39-53.21-47.21
=39.(53+43)+(-21).(53+47)
=39.96+(-21).100
=-1644
k cho minh
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15 +18+21+....+36+39+43
=(15 + 18+21+...+36+39) +43
áp dụng công thức tính dãy số ta có
(39-15):3+1 . (39 +15):2 + 43
= 9 . 27 + 43
= 81 + 43 = 124
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a, Ta có: 339 < 340 = (32)20 = 920
1121 > 1120
Vì 9 < 11 => 920 < 1120 => 339 < 1121
b, Ta có: 1245 - 1244 = 1244(12 - 1) = 1244.11
1244 - 1243 = 1243(12 - 1) = 1243.11
Vì 1244 > 1243 => 1244.11 > 1243.11 => 1245 - 1244 > 1244 - 1243
c, Đặt A = 1+2+22+....+29
2A = 2+22+23+...+210
2A-A=210-1
A=210-1
Ta có: 5.28 = 28.4 > 28.4 - 1 = 210 - 1
Vậy A < 5.28
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43 + ( 9 - 21 ) = 317 - ( x + 317 )
<=> 31 = 317 - x - 317
<=> 31 = -x
<=> x = -31
y-9+21=43+39
y-9+21=82
y-9=82-21
y-9=61
y=61+9
y=70
y-9+21=43+39
y-9+21=82
y-9 = 82 - 21
y-9 = 61
=> y = 61 + 9 = 70