According to the 24 point algorithm, there are four numbers 2, 3, 4 and 5. Each number is only operated once, and the result is equal to 24

According to the 24 point algorithm, there are four numbers 2, 3, 4 and 5. Each number is only operated once, and the result is equal to 24

(5+3-2)*4=24

Let the sum of the first n terms of a sequence an be SN. If SN is an equal ratio sequence with the first term S1, all the items are positive and the common ratio Q, the general term formula of an can be obtained
Denoted by S1 and Q

Sn=S1q^(n-1)
Sn-1=S1q^(n-2)
an=Sn-Sn-1=S1[q^(n-1)-q^(n-2)]
=S1[q^(n-2)(q-1)]
=S1q^(n-2)(q-1)
a1=S1
The general formula of sequence {an} is
an=S1 (n=1)
S1q^(n-2)(q-1) (n>1)

The perimeter of a square is 52 decimeters. What is the area of this square

52 / 4 = 13 (decimeter)
13 * 13 = 169 (square decimeter)
Answer: the area is 169 square decimeters

54 * (8 / 9-1 / 3-1 / 6)

54*（8/9-1/3-1/6）
=54*8/9-54*1/3-54*1/6
=48-18-9
=21

Let x1, X2,..., xn be positive integers. Prove (x1 + x2 +. Xn) (1 / X1 + 1 / x2 +. 1 / xn) > = n square

From Cauchy inequality original form > = (1 + 1 + 1 +...) + 1) ^ 2 = n ^ 2, note: This is the arithmetic mean ＞ = harmonic mean

Xiao Ming's living room needs 200 square bricks if it is 36 square decimeters, and how many square bricks if it is 100 square decimeters

1. Arithmetic: 36 × 200 △ 100 = 72 pieces
2. Inverse example method:
If you need 100 square decimeters, you need x pieces:
100x=36×200
x=72

The topic of sine and cosine theorem in Senior High School
1. Sinbcosc + cosbsinc = 2sinbcosc. How to sort out and simplify sin (B-C) = 0 & nbsp; 2. If sin2a = sin2b, then what kind of triangle is this. & nbsp; 3. What is the complementary relationship between sine and cosine? & nbsp; all the detailed process is needed

Sinbcosc + cosbsinc = 2sinbcosc moves to sinbcosc-cosbsinc = 0, C is changed to - C, sinbcos (- C) - cosbsin (- C) = 0, sin (B-C) = 0; 2. From the sum difference product formula: sin α - sin β = 2cos [(α + β) / 2] sin [(α - β) / 2], sin2a-sin2b = 2Sin (a-b) CO can be obtained

Judgment: y = half pie - arccosx is an odd function. The inverse function of y = SiNx is arcsinx

Y = dichotomous arccosx = arcsinx
So right
Y = SiNx is not a monotone function and has no inverse function
So wrong

Use 27 small cubes with 2 cm edge length to form a large cube, and calculate the surface area of the large cube
It can be calculated by formula

The length, width and height of the large cube are composed of three small cubes, so the side length of the large cube is 6cm, and the surface area is 6 * 6 * 6 = 216cm

A mathematical thinking problem
Both Party A and Party B go to the park at the same time. Party A travels 10km per hour and Party B 8km per hour. At 20km, Party A goes back to school to get things. Therefore, Party A arrives at the park one hour later than Party B. find out the distance between the school and the Park

If it's from school, it takes four hours for a to pick up things,
An hour later than B means 10km less walking,
That is to say: if a doesn't go to get things, he will walk 4 * 10-10 = 30km more than B,
A walks 2km more per hour than B, but 15 hours
15 * 8 = 120 km