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12 x 194+6x+3x369x4=
12x194+6x2x437+3x4x369=
12x194+12x437+12x369=
12x{194+437+369}=
12x1000=
12000
1+5+9+13+.....+57+61+65x2-6
={65+1}x4:2x2-6
=66x2x2-6
=132x2-6
=264-6
=258
a) \(1+5+9+...+65\)
\(=\frac{\left[\left(65-1\right):4+1\right].\left(65+1\right)}{2}=495\)
b) \(12.194+6.437.2+3.369.4\)
\(=12.194+12.437+12.369\)
\(=12.1000=12000\)
a) 35 x 34 + 35 x 38 + 65 x 75 + 65 x 45
= 35 x (34+38) + 65 x (75 + 45)
= 35 x 72 + 65 x 120
= 2520 + 7800 = 10320
b) 3 x 25 x 8 + 4 x 37 x 6 + 2 x 38 x 12
= 3 x ( 25 x 8) + 4 x (37 x 6) + 2 x (38 x 12)
= 3 x 200 + 4 x 222 + 2 x 456
= 600 + 888 + 912 = 2400
tk nha
35 x 34 + 35 x 38 + 65 x 75 + 65 x 45
= 35 x ( 34 + 38 ) + 65 x ( 45 + 75 )
= 35 x 72 + 65 x 120
a)12 x 18 + 14 x 3 - 255 : 17=25.58823529411765
b)68 + 42 x 5 - 625 : 25=5182
c) 13+ 21 x 5 - (198 : 11 - 8)=108
d) 1188 - 4 x (27 + 90 + 73 :10 )=
e) 5 + 8 + 11 + 14 +......+ 38 + 41=
f) 51 - 49 + 55 - 53 + 59 - 56 + 63 - 61 + 65=74
có mấy câu mình ko biết,xin lỗi bạn
Bài 1 :
a) ( 257 x 139 - 257 x 39 ) : 100
= 257 x ( 139 - 39 ) : 100
= 257 x 100 : 100
= 257
a) ( 257 × 139 – 257 × 39 ) : 100
= [ 257 x ( 139 -39 ) ] : 100
= ( 257 x 100 ) :100
= 25700 :100
=257
b) 5 + 6 + 13 + 17 + .......+ 2017
= ( 5 + 2017 ) + ( 6 + 2016 ) + ( 7 + 2015 ) + ... + ( 1009 + 1013 ) + ( 1010 + 1012 ) + 1011
= 2022 + 2022 + 2022 + ... + 2022 + 2022 + 1011
= 2022 × 1006 + 1011
= 203514
c) 12 × 57 + 57 × 15 + 63 × 57
= 57 × ( 12 + 15 + 63 )
= 57 x 90
= 5130
Bài 1:
\(A=\frac{1}{\left(1+2\right)}+\frac{1}{\left(1+2+3\right)}+\frac{1}{\left(1+2+3+4\right)}\)\(+\frac{1}{\left(1+2+3+4+5\right)}+...+\)\(\frac{1}{\left(1+2+3+...+10\right)}\)
\(A=\frac{1}{3}+\frac{1}{6}+....+\frac{1}{55}\)
\(A=2\left(\frac{1}{6}+\frac{1}{12}+....+\frac{1}{110}\right)\)
\(A=2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{10.11}\right)\)
\(A=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{10}-\frac{1}{11}\right)\)
\(A=2.\left(\frac{1}{2}-\frac{1}{11}\right)\)
\(A=\frac{9}{11}\)
Bài 2 :
2) Tử số = 11 x 13 x 15 + 3 x 3 x 3 x 11 x 13 x 15 + 5 x 5 x 5 x 11 x 13 x 15 + 9 x 9 x 9 x 11 x 13 x 15
= (1 + 3 x 3 x 3 + 5 x 5 x 5 + 9 x 9 x9) x 11 x 13 x 15 = (1+27+125+ 729) x 11 x 13 x 15
Mẫu số = 11 x 13 x 17 + 3 x 3 x 3 x 13 x 15 x 19 + 5 x 5 x 5 x 13 x 15 x 17 + 9 x 9 x 9 x 13 x 15 x 17 lớn hơn 11 x 13 x 15 + 3 x 3 x 3 x 13 x 15 x 17 + 5 x 5 x 5 x 13 x 15 x 17 + 9 x 9 x 9 x 13 x 15 x 17
= (1 + 3 x 3 x 3 + 5 x 5 x 5 + 9 x 9 x9) 13 x 15 x 17 = (1+27+125+729) x 13 x 15 x 17
\(\Rightarrow A< \frac{\left(1+27+125+729\right)\times11\times13\times15}{\left(1+27+125+729\right)\times13\times15\times17}\)
\(=\frac{11}{17}\)
\(=\frac{1111}{1717}=B\)
Vậy \(A=B\)
