A and B are moving in the same direction on the road at a constant speed. A's speed is 3 km / h, and B's speed is 5 km / h. A passes through place a at 12 noon, and B passes through place a at 2 pm. What time can b catch up with a in the afternoon? How far is it from ground a?

A and B are moving in the same direction on the road at a constant speed. A's speed is 3 km / h, and B's speed is 5 km / h. A passes through place a at 12 noon, and B passes through place a at 2 pm. What time can b catch up with a in the afternoon? How far is it from ground a?

According to the meaning of the question: 6 + 3x = 5x, the solution is: x = 3, 5 × 3 = 15 (km). Answer: B can catch up with a at 5 p.m., and the distance to a is 15km

It is known that A. B is positive R, and a + B = 1. It is proved that: (1 + 1 / a) (1 + 1 / b) is greater than or equal to 9
No, I haven't. We study basic inequalities.

Square of (radical a-radical b) ≥ 0
If multiplied, it is a + B-2 radical (AB) ≥ 0
That is, 1 = a + B ≥ 2 radical (AB), ab ≤ 1 / 4
(1+1/a)(1+1/b) = (1+a)(1+b)/ab = 2/ab+1 ≥ 2/(1/4)+1 = 9

The representation of derivative in Calculus
dy/dx dy/dx² d²y/dx²

The first derivative of dy / DX with respect to y
Dy / DX & # 178; the first derivative of Y with respect to X & # 178
D & # 178; Y / DX & # 178; for y, find the second derivative of X
Hope to help you!

High school politics: using the knowledge of cultural life to analyze the theoretical basis of building a strong province in Guangdong Province

① As a spiritual force, culture can be transformed into material force in the process of people's understanding and transforming the world, which has a profound impact on social development
② Culture and economy interact and blend with each other. Excellent culture can provide correct direction guarantee, inexhaustible spiritual power and strong intellectual support for economic construction
③ As culture and politics blend with each other, people need higher cultural literacy to participate in political life; meanwhile, the struggle against cultural hegemony has become an important part of international political struggle
④ Culture has increasingly become an important source of national cohesion and creativity, and an important factor in the competition of comprehensive national strength
⑤ Excellent culture can enrich people's spiritual world, enhance people's spiritual strength and promote people's all-round development

Differential of function y = sine ^ - x
Y = sine ^ - x for Dy

y=sine^-x
The derivation on both sides is very good
dy/dx=(cose^-x)*(e^-x)'
dy/dx=(cose^-x)*(e^-x)*(-x)'
dy/dx=(cose^-x)*(e^-x)*(-1)
therefore
dy=[-(cose^-x)(e^-x)]dx

It is known that α belongs to (0, π / 2), β ∈ (π / 2, π), sin (α + β) = 3 / 5, cos β = - 5 / 13, and Tan α is obtained

Because α belongs to (0, π / 2), β∈ (π / 2, π), so (α + β) ∈ (π / 2, 3 π / 2), so cos (α + β) = - 4 / 5, so tan (α + β) = - 3 / 4, and β∈ (π / 2, π), cos β = - 5 / 13, so sin β = 12 / 13, so tan β = - 12 / 5
tanα =tan[(α+β)-β]=[tan(α+β)-tanβ]/[1+tan(α+β)*tanβ]=33/56.

The denominator of a fraction is 3.75 times of the numerator, and the numerator is 11 times smaller than the denominator___ ．

Let the numerator of this fraction be x, then the denominator is 3.75x. From the meaning of the question, we can know that: 3.75x-x = 11, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 4, then the denominator is 4 × 3.75 = 15, then this fraction is 415; so the answer is: 415

On differential calculus of multivariate functions
Like this form of F (x, y, z) = 0, z = f (x, y)
Sometimes when seeking partial derivatives, such as partial derivatives of X, we need to treat y and Z as constants. Sometimes we only treat y as constants and Z as functions of X. what's the matter?
When is it to take y and Z as constants and find the partial derivative of X? When is it to take y as constants and Z as a function of X and find the partial derivative of X
Why do we sometimes treat y as a constant and Z as a function of X?

Why do we sometimes regard y as a constant and Z as a function of X? Because Z is a function of X, and f (x, y, z) = f (x, y, f (x, y)) to the right of the equal sign, independent variables are only x, y, that is to say, the change of X has no effect on y, the change of Y has no effect on X, and X and y are independent variables

If a + B + 2 and 2ab-1 are opposite to each other, find the value of a + B / 3ab-3ab / A + B + 1

If a + B + 2 and 2ab-1 are opposite to each other,
A + B + 2 + 2ab-1 = 0
a+b=-2
2ab=1
ab=1/2
a+b/3ab-3ab/a+b+1
=-2/(3x1/2)-(3x1/2)/(-2)+1
=-4/3+3/4+1
=-16/12+9/12+1
=5/12
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15 / 16 tons of coal will be transported in 5 times. How much coal will be transported each time? The formula of division is: (); the formula of multiplication is: ()

15 / 5 of 16
15 / 16 * 1 / 5