The maximum value of function y = X3 ^ - 3x on [- 2,2] is A.0 B.1 C.2 D.-2

The maximum value of function y = X3 ^ - 3x on [- 2,2] is A.0 B.1 C.2 D.-2

y=x3^-3x
y'=3x^2-3
In [- 2,2]
y‘>0
So the increasing function reaches the maximum at x = 2
2. Choose C

Please make up a practical problem according to your life, so that the equation listed is 3x + 20 = 4x-25

There is a class of students going on spring outing and boating. If there are 3 people in each boat, there are 20 people without seats. If there are 4 people in each boat, there are 25 people
Perhaps so, the landlord can add

There is a cylinder with a height of 10 cm. If the height of the cylinder is reduced by 2 cm, the surface area of the cylinder will be reduced by 12.56 square cm. How about the volume of the original cylinder?

The radius of the bottom of the cylinder is: 12.56 △ 2 △ 3.14 △ 2 = 1 (CM), 3.14 × 1 × 1 × 10 = 31.4 (cm3); a: the original volume of the cylinder is 31.4 cm3

The sum of ten natural numbers is equal to 1001. What is the maximum value of the greatest common divisor of these ten natural numbers___ ．

1001 is the sum of these natural numbers, that is, the multiple of the greatest common divisor of these ten natural numbers; 1001 = 7 × 11 × 13, so there are eight factors of 1001: 1, 7, 11, 13, 77, 91, 143, 1001.1001 △ 10 = 100.1, so the greatest common divisor of these ten numbers must be less than 100.1

α is the second quadrant angle. ① which quadrant is 2 α? Sin2 α > 0? ② if sin α + cos α ∈ (0.1), which quadrant is 2 α? Cos2 α > 0?
α is the second quadrant angle.
① Which quadrant is 2 α? Is sin2 α > 0?
② If sin α + cos α ∈ (0.1), which quadrant is 2 α? Is Cos2 α > 0

1. If α ∈ (π / 2 + 2K π, π + 2K π), then 2 α ∈ (π + 2K π, 2 π + 2K π) can belong to three or four quadrants, and sin2 α is absolutely less than 0
2. α is the second quadrant angle, sin α > 0, cos α < 0. If sin α + cos α ∈ (0.1), sin α is greater than the absolute value of cos α, cos square is less than sin square, cos square - Sin square = Cos2 α < 0, sin2 α = 2Sin α * cos α < 0, so 2 α is the third quadrant

I usually finish my homework from 9 o'clock to 10 o'clock on the first day of junior high school. Now I'm in the second day of junior high school. How long does it take for me to finish my homework? And keep the top 20?
How can we learn easily and do homework quickly? Is it hard or easy to write first? (don't tell me to listen carefully and review in class. I know all these.)

In my opinion, I will finish the simple writing first, and leave all the time for the difficult problems, so that I can think about the problems without worry. Otherwise, if I can't think of the difficult problems and have no time to write them, I will be anxious and can't devote myself to thinking. I will review the books and class notes before writing my homework, even if you think you have understood them all

If x and (- y) are opposite to each other and XY ≠ 0, what is 1910 x ^ 2 + 99 y ^ 2 / 2009 XY?

Because it's the opposite number
So let x = y = a
be
(1910a^2+99a^2)/-2009a^2
=2009a^2/-2009a^2
=-1

13 out of 19 minus 4 out of 11 plus 6 out of 19 minus 7 out of 11
Simple calculation

Hello: 13 / 19-4 / 11 + 6 / 19-7 / 11 = (13 / 19 + 6 / 19) - (4 / 11 + 7 / 11) = 1-1 = 0, which is the same as the ordinary calculation answer. ~ I'm glad to answer for you. If you have any other questions, please ask me. ~ 171819sss will answer for you at any time. ~ if you feel my answer is very good, please click [adopt

Given that x 2 + xy-2y 2 = 7, X and y are positive integers, try to find the value of X and y

∵ x2 + xy-2y2 = 7, ∵ (X-Y) (x + 2Y) = 7, ∵ x, y are positive integers, ∵ x − y = 1x + 2Y = 7 or X − y = 7x + 2Y = 1, the solution is x = 3Y = 2

In the first group, 6 people planted 15 trees; in the second group, 8 people planted 18 trees; in the third group, 5 people planted 15 trees
Which group planted more trees per person on average?

The third group
The average number of trees planted per person = the total number of trees planted per group △ the number of people in this group
The average number of trees planted in the first group was 15 △ 6 = 2.5
The average number of trees planted in the second group was 18 △ 8 = 2.25
In the third group, the average number of trees planted per person was 15 △ 5 = 3
The first group and the second group are less than 3 trees on average, so the third group plants more trees per person on average