Write down the sum 10 th term of the given sequence 23,21,19,....,5
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23,21,19,.....,5.
S10=?
a=23. d=21-23=-2. An=5.
An=a+(n-1)d.
5=23+(n-1)(-2).
5=23-2n+2.
-2n+25=5.
-2n=5-25.
-2n=-20.
2n=20.
n=20/2.
n=10.
Sn=n/2(a+An).
S10=10/2(23+5).
S10=5(28).
S10=140.
I think this is your answer. Please don't write as it is. I have typed capital letters in formulas.
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