Asked by bob

In a certain arithmetic sequence, t6 + t15 = –141 and the common difference is –7.
What is the first term of the sequence?

explain how to do this please
Answered by Reiny
you know t6 = a+5d
you know t15 = a+14d

so a+5d + a+14d = -141

don't you know d= -7 ???

take over ....
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