3 (X-7) + 5 (+ 8) = 15

3 (X-7) + 5 (+ 8) = 15

=-4/3 .

3 (X-7) + 5 (x + 8) = 15

The solution is 3 (X-7) + 5 (x + 8) = 15
We get 3x-21 + 5x + 40 = 15
That is, 8x + 19 = 15
The solution is 8x = - 4
That is x = - 1 / 2

A total of 350 tons of grain are stored in two warehouses A and B in a city. Now 50 tons of grain are transported from other places. The grain in warehouse B is 40 tons less than that in warehouse a three times
At present, cities a and B are suffering from disasters, and they need 150 tons and 250 tons of grain for disaster relief respectively. We know from the two grain depots A and B that the freight from grain depots a to cities a and B is 7 yuan / ton and 5 yuan / ton respectively, and the freight from grain depots B to cities a and B is 9 yuan / ton and 4 yuan / ton respectively. Please determine the lowest total transportation cost and find out the lowest total transportation cost?

After the transfer of 50 tons, Party A and Party B have a total of 400 tons. At this time, Party A's warehouse has: (400 + 40) / (1 + 3) = 110 tons, and Party B's warehouse has 400-110 = 290 tons. According to the requirements of the topic, Party a's warehouse will be transported to place a, 110 * 7 = 770 yuan, Party B's 40 tons to place a, 40 * 9 = 360 yuan, 250 tons to place B, 250 * 4 = 1000 yuan, totaling 2130 yuan

One math problem
The price of a lower garment is m yuan. A coat is 20 yuan less than twice the price of a lower garment. A coat is [] yuan
In a basketball game, Yao Ming hit a 3-pointer, B 2-pointer and got 3 free throws. In this game, he got a total of [] points
A ton of coal is transported from 3 canteen, and 0.5 ton is transported every day
Xiaohua paid a yuan to buy back three ballpoint pens, B yuan for each one, and there was still [
5. There are m refrigerators in the shopping mall. The purchase price of each refrigerator is a yuan and the selling price is B yuan. If all refrigerators are sold, the total profit will be [

It is clear that the price of a jacket is m yuan, and a jacket is 20 yuan less than twice the price of a jacket, and a jacket is [] yuan. If the jacket is n yuan, then n + 20 = 2m, n = 2m-202. In a basketball game, Yao Ming hits a 3-pointer, B 2-pointer, and 3 free throw. In this game, he gets a total of [] points

Mathematics problems of grade 5 in primary school (simple calculation of scores)
1：1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90
2：1/5×7 + 1/7×9 + 1/9×11 + 1/ 11×13 + 1/ 13×15
3：　6/1×7　－　6/7×13　－　6/13×19－　．．．－6/97×103
Now I understand the front, but the last one is different from what you did. Help me see if it's right
6/1×7　－　6/7×13　－　6/13×19－　．．．－6/97×103
＝（1－1/103）×1/2
＝102/103×1/2
＝51/103

1：1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90=(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)=1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10=1/3-1/10=7/302：1/5×7...

In an, A3 = 7, the first three terms and S3 = 21
a3=a1*q^2=7; (1)
s3=a1(1-q^3）/（1-q)=a1(1+q+q^2)=21; (2)
(2) (1) get
Q = 1, or q = - 1 / 2;
I want to ask (2) / (1) get 1 + Q + Q ^ 2 / Q ^ 2 = 3, then how to calculate?

(2) (1) get (1 + Q + Q ^ 2) / Q ^ 2 = 3
1+q+q^2=3q^2
2q^2-q-1=0
(q+1)*(2q-1)=0
Q = 1, or q = - 1 / 2;

Simple operation of 5 / 7 * 16 * 21 / 5

5/7*16*21/5=5/7*21/5*16=3*16=48

The shape of a triangle can be judged by knowing its three sides a, B.C; A2 + B2 + c2-2ab-2bc = 0

b^2-(2a+2c)b+(a^2+c^2)=0
B exists, then
Δ=（2a+2c）^2-4(a^2+c^2)=8ac
b=(a+c)±√（2ac）
Then a + C > B
therefore
b=(a+c)-√（2ac）
Then a + b > C, C < 2a and a < 2c are obtained
So C / 2 < a < 2C
b-a=c-√（2ac）=√c[√c-√2a]＜0
B < C, the same as B < a
When C < A
b^2+c^2-a^2=2√c*[√c-√(2a)](a+c)＜0
When a < C, B ^ 2 + A ^ 2-C ^ 2 < 0
So the triangle is a non isosceles obtuse triangle

62-1 = 63 move only one number to make the equation hold

62-1＝63
Put six to the power of two
2^6-1=63

It is proved that if a is a positive definite matrix of order n and B is a positive semidefinite matrix of order n, then a + B is a positive definite matrix

Any non-zero vector x Xax > = 0
For the same X xbx > 0
xAx+xBx>0
x(A+B)x>0
So a + B is positive definite