sequence

1. If the first term of an arithmeticsequence is 7 and the sum of the first 10 terms
is 325，find the 10thterm.
Sol
a1=7
S10=(a1+a10)*10/2
325=(7+a10)*5
a10=58

2. find the sum of the first 10 terms of an arithmetic sequence if its 4th termis 10
and the common difference is 2.
Sol
a4=a1+3d
10=a1+3*2
a1=4
a10=a1+9d=4+18=22
S10=(a1+a10)*10/2=(4+22)*5=130