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Anonymous users2024-02-07a1=5 6,(1 in the lower right corner)d = -1 6,sn=-5, (n in the lower right corner) find n and an (n in the lower right corner).
Solution: an=a1+d(n-1).
5/6-n/6+1/6
1-n/6sn=(a1+an)n/2
5/6+1-n/6)n/2
11-n)n/12=-5
i.e. 11n-n = -60
Solve this unary quadratic equation:
n²-11n-60=0
n-15)(n+4)=0
Get n = 15 or n = -4 (incompatibility).
i.e. n=15an=1-15 6=-3 2
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Anonymous users2024-02-06At the beginning of the year after A1.
After 2 years a-
After 3 years a- x-
10 years later a- x -
1) If in 10 years' time, the per capita housing area in the region doubles compared to today, how much more old housing should be demolished every year?
a-〖 x⋯-〖=2a
calculated as x=2) According to the demolition speed of (1), how many years will it take to demolish all the old rolling houses that need to be demolished? Year.
Therefore, it will take more than 18 years to dismantle it.
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Anonymous users2024-02-05Ratio: (a3) 2=a1xa4, (a2+d) 2=(a2-d)(a2+2d), (a2) 2+2da2+d 2=(a2) 2+da2-2d. d is not zero, and can be divided by d:
2a2+d=a2-2d，2a2-a2=-d-2d，a2=-3d=-3x2=-6。
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Anonymous users2024-02-04a(n+1)-an=3n+2
an-a(n-1)=3(n-1)+2
a2-a1=3✖️1+2
Add the above formula, add it to the left and add it to the right.
a（n+1）-a1=3【n（1+n）/2】+2nan=3/2【n（n-1）】+2n+1
You can just merge the formula on the right.
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Anonymous users2024-02-03a3=4
Specifically, A3 is the basis. Using the equation of the equal difference series: an=an-1+d, then there is a4 = a3+d
a5=a3+2d
a1=a3-2d
a2=a3-d
Add the above four mathematical equations together, and there is 5a3=20At this point, the answer is clear.
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Anonymous users2024-02-02Assuming there are x people, there are a total of 3x+1+2+3+...x-1）=100x
3x+x(x-1)/2=100x
x^2-x=194x
x^2-195x=0
x=0 (rounding) or x=195 (in line with the topic).
At this time, there are 195 * 100 = 19,500 table tennis balls.
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Anonymous users2024-02-01Solution: There are x people, 100x=3+4+.x+2）x=195
Count the rest yourself, it's always going to be.
Add an-1 on both sides of the recursive type
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