If you travel 30 kilometers an hour, you will arrive 15 minutes earlier than the train. If you travel 18 kilometers an hour, you will arrive 15 minutes later than the train? Can explain

If you travel 30 kilometers an hour, you will arrive 15 minutes earlier than the train. If you travel 18 kilometers an hour, you will arrive 15 minutes later than the train? Can explain

Let the whole distance be s and the train speed be v
(simultaneous equation) s / 30 + 15 = s / V
S/18 - 15 = S/V
The solution is s = 1350km, v = 22.5km/h
Let's set the following velocity as v2
1350/V2 +10 = 1350/22.5
Then V2 = 27km / h
Answer:

How to do the math problem 2|3 + (- 4|5) - 1|5 = (- 1|3) in the first exercise book of junior high school?

=-2/3

Let f (x) be continuous at x = 0 and f (x) / X limit exist when x approaches 0. It is proved that f (x) is continuous and differentiable at x = 0

Limf (x) / X exists, denominator -- > 0, so limf (x) = 0, f (x) is continuous at x = 0, limf (x) = f (0) = 0
F '(0) = Lim [f (x) - f (0)] / [x-0] exists, so f (x) is continuous and differentiable at x = 0

Solution equation: 7 (3 + x) = 21 (2) () 15 1 -------- = -------- = -------- (3) 24 ()
solve equations:
7（3+x）=21
2
（2） （ ） 15
1-------- =---------=--------
（3） 24 （ ）
The second question is why

7（3+x）=21
3+x = 3
x=0
2
(2） （40 ） 15
1-------- =---------=--------
（3） 24 （ 9 ）
【1+2/3 = 5/3 = 40/24 = 15/9 】

Find the rules (), (), 15, 13, (), 9, (), 3, 1

1. If there is only one bracket after 3, (21), (19), 15, 13, (11), 9, (5), 3, 1

The nth power of sequence an = n, BN = 1 / 2, find the value of A1B1 + a2b2 +... Anbn

Sn = A1B1 + a2b2 +... Anbn = 1 * (1 / 2) + 2 (1 / 4) + 3 (1 / 8) + 4 (1 / 16) +. N (1 / 2 ^ n) ① 1 / 2Sn = 1 * (1 / 4) + 2 (1 / 8) + 3 (1 / 16) + 4 (1 / 32) +. N (1 / 2 ^ (n + 1)) ② - ② 1 / 2Sn = 1 / 2 + 1 / 4 + 1 / 8 + 1 / 16 +... + 1 / 2 ^ N-N (1 / 2 ^ (n + 1)) = [2 ^ (n + 1) - n-2] / (...)

The original function of main 2 / X in calculating definite integral ∫ [1,2] (e ^ X-2 / x) DX will not be solved

∫ 1/xdx=In|x|+c
∫ [1,2](e^x-2/ x)dx = ∫ [1,2]e^xdx-2∫ [1,2](1/x)dx=∫ [1,2]e^x-2∫ [1,2]In|x|=∫ [1,2](e^x-2In|x|)=e^2-2In2-e

() + 3x = 16.94.8x + () = 27.781.5x + () x = 18 x - () x = 5 / 8 fill in the brackets with appropriate numbers

(1.9 )+3X=16.9
4.8X+( 22.98)=27.78
1.5X+(0.5 )X=18
X-(3/8 )X=5/8
You can understand, agree

Given that a is a normal number, when n is a natural number, the inequality | 2n / (n + 1) - 2|

∵ n∈N
∴ 2n/(n+1)

In 4, - 1.5,0,3.7, - 5 / 3,20, - 1 / 5, - 2294, () is a positive number, () is a negative number, () is a natural number

(4,3.7,20294) are positive numbers, (- 1.5, - 5 / 3, - 1 / 5, - 2) are negative numbers, and (4,0,20294) are natural numbers