Calculation ① (3x-2) (4x + 5) ② (1 / 3x-1 / 2Y) (1 / 2y-1 / 3x)

Calculation ① (3x-2) (4x + 5) ② (1 / 3x-1 / 2Y) (1 / 2y-1 / 3x)

①(3x-2)(4x+5)
=12x^2+15x-8x-10
=12x^2+7x-10
②(1/3x-1/2y)(1/2y-1/3x)
=1/6xy -1/9x^2 -1/4y^2 +1/6xy
=1/3xy -1/9x^2 -1/4y^2

How to solve the equation 3x + 2Y = 39,4x-3y = 18

3x + 2Y = 39 4x-3y = 18 multiply the two sides of the first formula by 3 and the two sides of the second formula by 2

The solution of the equations 3x + 2Y = m + 1,4x + 3Y = M-1 is greater than 0, and M is an integer. Try to find the value of (x + y) &# 178; - 1000 (x + y) - 2-m
Please use ∵, ∵, concise over some unnecessary words, love tiger oil

∵4x+3y=m-1 (1)
3x+2y=m+1 (2)
(1) - (2) get
x+y=-2
∴(x+y)^2-1000(x+y)-2-m=4+2000-2-m=2002-m
The problem comes down to finding the value of M
It is easy to get from (1) (2)
x=m+5,y=-m-7
∵ xy>0
Ψ m + 5 > 0 and - M-7 > 0
perhaps
m+5

If S4 = 2240, A2 + A4 = 180, then A1=

A2 + A4 = A2 (1 + Q & # 178;) = 180s4 = 240 = A2 + A4 + A1 + a3 = 180 + A1 + a3, so a1 + a3 = 60, and a1 + a3 = A1 (1 + Q & # 178;) = 60, so q = A2 / A1 = A2 (1 + Q & # 178;) / A1 (1 + Q & # 178;) = 180 / 60 = 3, so A1 (1 + 3 & # 178;) = 60, A1 = 60 / 10 = 6

98766 out of 98765, 9876 out of 9877, 987 out of 988, 98 out of 99

Reverse the order is from small to large, the first is the largest, and no matter the first is 98766 of 98765 or 98765 of 98766, it is the first largest, followed by the last one

In the quadrilateral ABCD, e and F are the midpoint of AD and BC respectively, and G and H are the midpoint of BD and AC respectively

Certification:
Connect g, F, h and e successively to form a quadrilateral
Because g and F are the midpoint of BD and BC respectively
So GF is the median of triangle BCD
So GF ‖ CD and GF = CD / 2
Similarly, it can be proved that he ‖ CD and he = CD / 2
So GF ‖ he and GF = he
So the quadrilateral gfhe is a parallelogram
So GH and EF are equally divided
For reference! Jswyc

4 13 8 1 = 24 fill in the operation symbols or brackets in the following groups to make the equation true

4 ×﹙13 －8 ＋1﹚=24

Given the inverse matrix a − 1 = − 143412 − 12 of matrix A, the eigenvalues of matrix A are obtained

Because a-1a = e, a = (A-1) - 1. Because | A-1 | = - 14, a = (A-1) - 1 = 2321 So the characteristic polynomial of matrix A is f (λ) =. λ − 2 − 3 − 2 λ − 1. = λ 2-3 λ - 4 Let f (λ) = 0, the eigenvalue of a is λ 1 = - 1, λ 2 = 4 (10 points)

The sum of all the four digits of 24 is called "ad". In the four digits of Xiaoyu 2000, how many such books are there?

24-1 = 23, the sum of the remaining three digits is 23. 23 = 9 + 9 + 5 = 9 + 8 + 6 = 8 + 8 + 7 = 9 + 7 + 7, there are 3 + 6 + 3 + 3 = 15

On the determinant of block matrix: det (a + I) = det (a)?
Because: [I - I, O, I]. [(a + I) O, O, I]. [I, O, I] = [a, O, I]. So there is: det [I - I, O, I]. Det [(a + I) o, O, I]. Det [I, O, I] = det [a, O, I]. So there is: det (a + I) = det (a). This is obviously wrong, why? (above det is the evaluation symbol of matrix determinant, I is the symbol of unit matrix.)

Calculation error
[I - I, O I]. [(a + I) O, O I]. [I O, I I] = [a - I, I I]. Not [I - I, O I]. [(a + I) O, O I]. [I O, I I] = [a o, I]