Question 1159332
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a1 = 1 is the first term
d = 2 is the common difference, telling us to add 2 to each term to get the next one


nth term of an arithmetic sequence
a(n) = a1 + d(n-1)
a(n) = 1 + 2(n-1)
a(n) = 1 + 2n-2
<font color=red>a(n) = 2n - 1</font>


It looks like you have the right idea when you wrote 1+2(10), though the "10" should be n-1, and then you simplify to what you see above.
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