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There is an arithmetic sequence: 3, 7, 11, 15 The 100th term of this arithmetic sequence is______ ．
3 + (100-1) × 4 = 3 + 396 = 399, so the answer is: 399
It is known that the third term of the arithmetic sequence is equal to 9 and the ninth term is equal to 3. Find the sum of the first nine terms of the arithmetic sequence
(a9-a3)/(9-3)=(a3+6d-a3)/6=d=(3-9)/6=-1
a3=a1+2d
a1=9-2d=9+2=11
S9=(a1+a9)/2*9=(11+3)/2*9=63
Find arithmetic sequence 3,5,7,9 Items 10 and 100 of
Be complete
Item 10 3 + 2 * (10-1) = 21
Item 100 3 + 2 * (100-1) = 201
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