There are x story books in the bookstore. The number of science and technology books is 1.2 times of that of story books, and the number of science and technology books is 1.2 times______ The number of literature and art books is 100 less than 3 times of the story, and the number of literature and art books is 100______ Ben

There are x story books in the bookstore. The number of science and technology books is 1.2 times of that of story books, and the number of science and technology books is 1.2 times______ The number of literature and art books is 100 less than 3 times of the story, and the number of literature and art books is 100______ Ben

(1) X × 1.2 = 1.2x (Ben); (2) x × 3-100 = 3x-100 (Ben)

Mr. Wang went to the bookstore and bought five of the same story books and five of the same math books. The salesman said that he should pay 43.38 yuan in total. Mr. Wang said that the salesman had miscalculated
Think about it, how does Mr. Wang know!

43.38 is not a multiple of 5

Given that y = x / LNX is the solution of the differential equation y '= Y / x + φ (x / y), then the expression of φ (x / y) is?
A.-(y^2)/(x^2)
B.(y^2)/(x^2)
C.-(x^2)/(y^2)
D.(x^2)/(y^2)

Don't you just go in and replace it
y'=(lnx-1)/(lnx)^2
φ(x/y)=y'-y/x=(lnx-1)/(lnx)^2-1/lnx
=-1/(lnx)^2=-y^2/x^2
A

The equation AX ^ 2 + AX-2 = 0 has a solution on [- 1,1]. Find the value range of real number a
I do this: a = 0, does not hold. Then the following is A0, but the teacher said a > 0 can not, f (- 1)

X = 0, x = - 1 is not the solution of the equation, because there is a solution, so a = 2 / (x ^ 2 + x) (x is not equal to 0, - 1) is within (- 1,0), and the value range of x ^ 2 + X is (- 1 / 2,0), so a = 2 / (x ^ 2 + x) is within (- ∞), - 4) is within (0,1], and the value range of x ^ 2 + X is (0,2), so the value range of a = 2 / (x ^ 2 + X) is [1, + ∞) and the value range of a is a

150 times 46 column vertical calculation

The concept of high number limit
Why should limit 2sinx-sin2x be reduced to 2sinx (1-cosx) instead of directly bringing in 2sinx = 2x and sin2x = 2x?

This paper deals with the application of Taylor Mean Value Theorem. In fact, the equivalent substitution we use is only an approximate substitution
SiNx ~ x, the exact replacement should be: SiNx = X-1 / 3! X ^ 3 + O (x ^ 3), followed by a series of infinitesimals higher than x
It's like a fight between 2sinx and sin2x. The eldest is 2x, and they all bring a group of younger brothers. The eldest is dead. Who wins depends on the younger brother's ability of course
And your problem is that the boss can win if he is strong, but he is not as strong as the boss

Given that the quadratic equation 4x-3y = 21, X and y are opposite to each other, what is y = then?

Depressed ~ this is also used to test ~ it's not enough to change x into - y ~ - 7Y = 21. How much do you say y = ah?

1.1+1.12+1.123+1.1234+1.12345+1.123456+1.1234567+1.12345678+1.123456789=

10.08367627

On the problem of y = 0 in the method of logarithmic derivation in higher numbers
Let y = f (x) y ＞ 0 and Y ＜ 0 have the same value by logarithmic derivation method respectively, then the point of y = 0 can't be done by logarithmic derivation method. But why does the result of y = x ∧ 3 by logarithmic derivation method hold for y = 0? Is it a coincidence or inevitable? In the future, all the functions of Y belonging to r only calculate the derivative of Y ＞ 0, Is y = 0 automatically included in it?
I think it is because we know that the derivative function of y = x ∧ 3 is continuous, so we can classify y = 0 as Y > 0

Let y = f (x) y ＞ 0 and Y ＜ 0 be the same value with logarithmic derivation method respectively, then the point of y = 0 cannot be done with logarithmic derivation method, right?
correct
But why does a function like y = x Λ 3 also hold for y = 0 by logarithmic derivation? Is it coincidence or inevitable?
This function doesn't need logarithmic derivation at all!
Logarithmic derivation is only used in the case of y = x ^ x, that is, the base and index have independent variables

How to understand 1-20 relation expression, the result of operation is "true"

This symbol means not equal to