Soldato
Hi guys, got a question here that i can't seem to make sense
The sum of the first 12 terms of an AP is 222, the sum of the first 5 terms is 40. Write out the first four terms of the series.
Right I'm using te Sn=n/2[2a+(n-1)d] equation to form a simultaneous equation to work out a and d:
222=6[2a+11d]
40=5/2[2a+4d]
Multiplying the brackets leaves me with:
222=12a+66d
40=5a+10d
Multiplying the first one by 5 and the second by 12 to get a common a of 60 lets me find d, but it doesn't give me the right answer. for the record, a is 2 and d is 3, but i can't get those answers. I know I've obviously done something silly, or might even be doing the completely wrong thing, can someone point me in the right direction please?
The sum of the first 12 terms of an AP is 222, the sum of the first 5 terms is 40. Write out the first four terms of the series.
Right I'm using te Sn=n/2[2a+(n-1)d] equation to form a simultaneous equation to work out a and d:
222=6[2a+11d]
40=5/2[2a+4d]
Multiplying the brackets leaves me with:
222=12a+66d
40=5a+10d
Multiplying the first one by 5 and the second by 12 to get a common a of 60 lets me find d, but it doesn't give me the right answer. for the record, a is 2 and d is 3, but i can't get those answers. I know I've obviously done something silly, or might even be doing the completely wrong thing, can someone point me in the right direction please?
