Answer:
90
Step-by-step explanation:
To find s4 we find sum of values when n=1,n=2,n=3,n=4
given expression is 
n=1 , plug in 1 for n

n=2

n=3

n=4

Sum of all 4 terms = 6+12+24+48=90
Step-by-step explanation:
with your square root symbol I never know what is inside the square root and what is possibly outside.
so, I can only guess and see what comes close.
f(x) = 2x² + x - 1
g(x) = sqrt(2x - 1) ??? is that so ?
h(x) = -2
2g(f(x)) + h(x)
g(f(x)) means that the whole f(x) expression is used as x in g(x).
the whole combined function is then
2×sqrt(2(2x² + x - 1) - 1) - 2
2×sqrt(4x² + 2x - 2 - 1) - 2
2×sqrt(4x² + 2x - 3) - 2
and if I am not mistaken, then this is the solution you mentioned at the beginning (if I try to read between the typos and missing info).
this is how people get to this.
do you understand it now ? or is there still something unclear ?
Answer:
5381.6
Step-by-step explanation:


P=2(l + b)
P=2l + 2b
P-2b=2l
P-2b/2=l
C is your answer