the formula is
[tex] \frac{a_1(1-r^n)}{1-r} [/tex]
a1=first term
n=which term
r=common ratio
we see the common ratio is -2
frs term is 1
and we go to 10th term so n=10
[tex] \frac{1(1-(-2)^{10})}{1-(-2)} [/tex]
[tex] \frac{1(1-1024)}{1+2} [/tex]
[tex] \frac{1(-1023)}{3} [/tex]
-341
the sum is -341
