Question
how many terms of the series -8,-6-,-4.... make the sum 90?
Answers
Reiny
a=-8
d=+2
n=?
S(n) = n/2[2a+(n-1)d]
90 = n/2[-16 + 2(n-1)]
this works out to
n^2 - 9n - 90 = 0
this factors nicely and has two answers, one of which will make no sense.
Let me know what you got.
d=+2
n=?
S(n) = n/2[2a+(n-1)d]
90 = n/2[-16 + 2(n-1)]
this works out to
n^2 - 9n - 90 = 0
this factors nicely and has two answers, one of which will make no sense.
Let me know what you got.
shree
To be smart in math
shree
To be smart in matj.