I bought two sets of books, each of which cost 22 yuan. How many books are there in each set

I bought two sets of books, each of which cost 22 yuan. How many books are there in each set

(2.5+3)x=22,x=4

There are 140 books in the library, 80% of which are literature and art books. How many other books are there?

140×（1-80%）=140×20%
=28

There are 75 science and technology books and 60 literature and art books in the sixth (third) class library corner. What percentage of science and technology books are literature and art books? How many percent less literature books than science and technology books?

60 △ 75 = 80%; 1-80% = 20%; a: literature and art books are 80% of science and technology books, 20% less than science and technology books

Known complete set u = {1,2 , 9,10}, a = {1,3,5}, B = {2,4,6,8}, find CUA, cub, a ∩ cub, a ∪ cub, Cu (a ∩ cub)
Cu(A∩B）,Cu(A∪B) .

CuA={2,4,6,7,8,9,10}
CuB={1,3,5,7,9,10}
A∩CuB =｛1,3,5｝
A∪CuB = CuB = {1,3,5,7,9,10}
Cu(A∩B）= U
Cu(A∪B) = {7,9,10}

Given the line segment CD, extend CD to B so that DB = 1 / 2CB, extend CD to a reversely so that Ca = CB, if AB = 12, find the length of CD

DB=1/2CB
D is the midpoint of BC, CD = BD
Extend CD to a reversely so that Ca = CB
C is the midpoint of AB, AC = BC
CD=1/4AB=3

Let 1xn matrix Y = [1 / 2,0,..., 0,1 / 2] a = the inverse of e-y, and the inverse of B = e + 2Y, XY e, be the unit matrix of order n, and find ab
How to ask

Note: in the title "a = e-y inverse matrix XY". Y is 1xn matrix, should be y transpose y '!
First, YY '= 1 / 4 + 1 / 4 = 1 / 2
therefore
AB = (E - Y'Y)(E + 2Y'Y)
= E +Y'Y - 2Y'(YY')Y
= E + Y'Y - Y'Y
= E.

The range of y = x2 − x + 12x2 − 2x + 3 is______ ．

Let x2-x + 1 = t, (X-12) 2 + 34 = t, so t ≥ 34  y = x2 − x + 12x2 − 2x + 3 = T2T + 1 = 12 + 1t < 12, when t = 34, 1t is the maximum, then y is the minimum, y = 12 + 1T = 310, so the range of y = x2 − x + 12x2 − 2x + 3 is [310, 12]. So the answer is: [310, 12]

Sin ^ n x * cos ^ m x from 0 to 2pi
The first step of the answer is to say "it can be obtained from the integral property of periodic function", and then change the integral limit to - pi to PI, and the rest remain unchanged?
The second step of the answer is "when n is odd, the integrand is odd, so the integral is equal to 0". Why is the integrand odd? What are the parity conclusions of sin ^ n x and COS ^ n x?
The third step of the answer "when m is an odd number, M = 2K + 1" is reduced to sin ^ n x * (1-xin ^ 2 x) ^ k dsinx & nbsp; & nbsp; in the integral from - pi to + PI, then how can this formula be equal to 0?
The answer is too brief

1. Periodic function, the integral in any period is the same; 2. The period of SiNx, cosx is 2 π, the integral from 0 to 2 π, and the integral from - π to + π cover the 2 π interval, and the integral value is the same; 3. SiNx is an odd function, cosx is an even function, and the result is an odd function multiplied by an even function

There are four different numbers. The sum of them is the product of their multiplication. What are these four numbers?

There seems to be no solution to this problem
1 * 2 * 3 * 4 are 24
but
If any number is OK, there are many answers
-1 -2 0 3；
As long as it contains 0; as long as the remaining three numbers add up to 0
Embarrassed

Calculation formula of cylinder volume

V = circumference × square of radius × height = π R & # 178; H