The problem asks to find $u_{50}$ and $S_{50}$ for an arithmetic sequence given that $u_2 = 6$ and $u_{10} = 22$. Here, $u_n$ represents the nth term and $S_n$ represents the sum of the first n terms of the arithmetic sequence.

ArithmeticArithmetic SequencesSeriesSummationnth term
2025/4/3

1. Problem Description

The problem asks to find u50u_{50} and S50S_{50} for an arithmetic sequence given that u2=6u_2 = 6 and u10=22u_{10} = 22. Here, unu_n represents the nth term and SnS_n represents the sum of the first n terms of the arithmetic sequence.

2. Solution Steps

First, recall the formula for the nth term of an arithmetic sequence:
un=a+(n1)du_n = a + (n-1)d, where aa is the first term and dd is the common difference.
We are given that u2=6u_2 = 6 and u10=22u_{10} = 22. Therefore:
u2=a+(21)d=a+d=6u_2 = a + (2-1)d = a + d = 6 (1)
u10=a+(101)d=a+9d=22u_{10} = a + (10-1)d = a + 9d = 22 (2)
Subtract equation (1) from equation (2):
(a+9d)(a+d)=226(a + 9d) - (a + d) = 22 - 6
8d=168d = 16
d=2d = 2
Substitute d=2d=2 into equation (1):
a+2=6a + 2 = 6
a=4a = 4
Now that we know a=4a=4 and d=2d=2, we can find u50u_{50}:
u50=a+(501)d=4+(49)(2)=4+98=102u_{50} = a + (50-1)d = 4 + (49)(2) = 4 + 98 = 102
Next, we need to find the sum of the first 50 terms, S50S_{50}. Recall the formula for the sum of the first n terms of an arithmetic sequence:
Sn=n2(a+un)S_n = \frac{n}{2}(a + u_n)
Therefore,
S50=502(a+u50)=502(4+102)=25(106)=2650S_{50} = \frac{50}{2}(a + u_{50}) = \frac{50}{2}(4 + 102) = 25(106) = 2650

3. Final Answer

u50=102u_{50} = 102
S50=2650S_{50} = 2650

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