Question

Find the sum of the summation of 2 i minus 9, from i equals 3 to 10 .

Answer 1

Sn = (n/2)(a1+an)

you have 8 terms from i = 3 to 10 (term 3,4,5,6,7,8,9,10) so n = 8

to find a1, plug in n = 3 into the sequence 2i - 9
to find an, plug in n = 10 into the sequence 2i - 9

then calculate Sn

Answer 2

i don't understand.. where would i plug the 3 into for the sequence 2i-9?

Answer 3

oh whoops meant to say i = 3 and i = 10 since i is the index not n

so you would just let i = 3 and calculate 2i - 9

Answer 4

oooohh okay! thank you

Answer 5

so it'd be; Sn=(8/2)(-3+11).. am i doing this right so far?

Answer 6

yes, then you would just evaluate that product

Answer 7

so the answer would be Sn=32.?

Answer 8

yup good

Answer 9

thank you so much!