Original post by TVIO
Use the formula for the sum of an arithmetic series for the 3 first values. Use the formula for Un=U20 = -32. Solve simultaneously.
I did the formula and got 3a+3d=12. So what do I do now?
Original post by Year11guy
I did the formula and got 3a+3d=12. So what do I do now?
You know that the 20th number is -32, so use the formula for Un and use it for U(20) = -32
Original post by TVIO
You know that the 20th number is -32, so use the formula for Un and use it for U(20) = -32
Thanks for the help, I've worked it out now!
Original post by Year11guy
Thanks for the help, I've worked it out now!
Glad to help! I personally found some of those sequences questions the hardest things in the course as you have to be really careful with them.
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