The master of mathematics is in the middle of the problem!!!

Solution: Set the number of classes to n

1+2+3+..n-1)=120 equal difference series.

and (first and last) the number of items 2

120=[1+(n-1)]×n-1)÷2

n 2 - n - 240 = 0 2 is squared.

n-16)(n+15)=0

n=16 n=-15 (no negative rounding).

A: There are 16 classes in total.

Good luck. Jilin Wang Qing llx

There were 120 matches in total, compared to 240 games against each team.

Since each team has to play one game against the other team, 16 15 = 240 so there are 16 teams in total.

Solution: Set up a team with x.

x(x-1)=120×2

x=16 (x=-15 discord).

A: There are 16 teams in total.

Solution: There are x classes in total. A total of (x-1) + x-2) + x-3) ......2+1=120。

That is, 1+2+3+....x-2) + x-1) + x-x=120 is summed by a number sequence.

That is, x(x+1) 2-x=120x*x-x-240=0 solves x=16, x=-15 (not in place, discard).

So this school has a total of 16 classes.

Don't forget to give points, thank you.

“！"In mathematics, it means factorial.

That is, multiply from one order to another, and multiply until 1.

Here 98! You can get 100*99 by dividing it

(1)a2=a1q=2;

a5=a1q^4=16

a5/a2=q^3=8

q=2, a1=1

an=a1q^(n-1)=2^(n-1);

2)b1=a5=16; b8=a2=2b8-b1=7d=-14

d=-2;bn=b1+(n-1)d=16-2(n-1)=18-2nsn=(b1+bn)*n/2=17n-n^2=-(n-17/2)^2+(17/2)^2

So when n = 8 or 9, sn has a maximum value of 72;

It can also be understood in this way, bn=18-2n; n=9 is bn=0 when n is large, bn is negative, and sn begins to decrease, so sn=8 or 9 has a maximum value of sn;

My tutor is coming soon, ask someone to answer! A works 1 20 and B is 1 14, so if you take two hours as a unit, every two hours will complete 17 140, 8 units, and 16 hours will complete 136

Let Li Ying's original money be x, and Wang Qiang's original money is y, and there are 2 5x=3 8y, then 16x=15y, y>x, so Wang Qiang originally brought more money.

Let y=ax 2+bx+c

Find the coordinates of a, b, and c:

a(,0),b(,0),c(0,0,a,b,c

The function image opens upward, and the axis of symmetry is x=(a-1) 2 from the meaning of the title, (a-1) 2<=1 2, so a<=2f(2)=4-2(a-1)+5=11-2a>=11-2*2=7, you are zero "points", thank you...