im creating a program which sums the values in a sequence, but it has alternate plus/minus.
I want to make the sum of this sequence 1-(1/3)+(1/5)-(1/7)....How can i use an alternate plus and minus just like the previous example?
Here is the code i have made so far:
s=input("Ingrese el numero de terminos a sumar:", )
for i in xrange(1,s+1):
print "La suma de los",s,"terminos es %.2f"%(sum)
You can raise
-1 to the power corresponding to the index of whatever term you're on:
>>> (-1)**0 1 >>> (-1)**1 -1 >>> (-1)**2 1 >>> (-1)**3 -1 >>> (-1)**4 1
Hence, the whole summation can be simplified to
result = sum((-1)**i * 1.0/(2*i + 1) for i in xrange(s))
(You shouldn't use
sum as a variable name, since the name is already taken by the built-in function
sum I used above.)