Asked by bilal qureshi

how many terms of the series -8,-6-,-4.... make the sum 90?
Answered by 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.
Answered by shree
To be smart in math
Answered by shree
To be smart in matj.
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