When calculating decimal addition and subtraction, be sure to align the same digits______ (judge right or wrong)

When calculating decimal addition and subtraction, be sure to align the same digits______ (judge right or wrong)

According to the calculation method of decimal addition and subtraction, when calculating decimal addition and subtraction, we must pay attention to align the same digits

Fraction, decimal addition and subtraction, 300 channels

1 / 2 + 1 / 3 = 1 / 3 + 1 / 4 = 1 / 4 + 1 / 5 = 1 / 5 + 1 / 6 = and so on
0.1 + 0.2 = 0.2 + 0.3 = 0.3 + 0.4 = 0.4 + 0.5 = and so on

A cylindrical water pipe, 20 cm in diameter, the speed of water flow is 4 meters per second, how many cubic meters of water can this pipe flow in one minute

π * 0.1 * 0.1 * 4 = 0.04 π m3 / s, one minute is multiplied by 60, that is, water flowing through 2.4 π m3

Proof of infinitesimal y = x / (1 + x)
It is proved by definition that y = x / (1 + x) is infinitesimal when x tends to 0
This is a theorem, not a definition of infinitesimal

f(x)=x/(1+x) ,
Because f (x) → 0 (when x → 0)
So for ∨ ε > 0, З δ > 0

Think about it and fill in 3.6.9 (). (). 19.17.15 (). (). (). 5
Think about it and fill it in
3.6.9（）.（）.（）.
19.17.15.（）.（）.（）.
5.10.（）.20 .

12, 15, 18 the middle is three
In the middle of 13, 11 and 9, there is a decrease of 2
The middle of 15 is 5
Thank you. I hope you will accept

Those that can be calculated by simple method should be calculated by simple method. 25 × 1.25 × 32 & nbsp; (3.75 + 4.1 + 2.15) × 9.85400-2940 △ 28 × 27 (20.2 × 0.4 + 7.88) △ 4.2 (45 + 14) △ 73 + 710 & nbsp; & nbsp; 10 △ 83 - (513 △ 526 + 25)]

（1）25×1.25×32，=（25×4）×（1.25×8），=100×10，=1000；（2）（3.75+4.1+2.15）×9.8，=10×9.8，=98；（3）5400-2940÷28×27，=5400-105×27，=5400-2835，=2565；（4）（20.2×0.4+7.88）÷4.2，=（8.08...

When the angle between them is 90 degrees, the resultant force is F. when the angle between them is 60 degrees, the reasonable size is f
A. 2F B, (radical 6 / 2) F C, (radical 2 / 2) F D, (radical 3 / 2) f

When f = cos45 (F1 + F2) 60 ° f = cos30 (F1 + F2), so we get the answer B

How much is × - 0.8 × - 60 = 16. How much is ×

2 mathematical problems: fill in the following data according to the arrangement rules: (1) 12 / 1, 4 / 1, (), 4 / 9, (), 4 / 81, 4 / 243
（2）4,1,（ ）,16/1,64/1,（ ）
Smart people should help before school,

The first is 4 / 3
The second is 4 / 27
Rule: the numerator is 4, and the denominator is 3 ^ - 1, 3 ^ 0, 3 ^ 1, 3 ^ 2, 3 ^ 3, 3 ^ 4, 3 ^ 5

The prime numbers between 10 and 20 are () in which the digits on () and the digits on 10 are still the same
The prime numbers between 10 and 20 are () in which the number on () is still a prime number after exchanging the position with the number on 10.

Prime numbers between 10 and 20 are (11,13,17,19)
Among them, the numbers in (11,13,17) bits are still prime numbers after exchanging positions with the numbers in ten bits
11,31,71