The series is -10-2+6+14+...+110
We see that the common ratio is 8, so it is of the form T0+8n
We also see that T0=-10 (i.e. when the pattern starts.
So we have
Tn=-10+8n
and the summation would be
∑ (-10+8n)
Next to determine the limits.
We know that the first term is -10, which fits T0=-10+8(0).
The last term is 110, which gives the equation Tn=110=-10+8(n)
Solving for n gives
n=(110+10)/8=15
Therefore the limits of summation are 0, 15
hence the summation formula is
[tex]\sum_0^{15}(-10+8n)[/tex]
I will leave the other problem you posted for your own exercise.
