In an AP , first term is 24 and common difference is -4, find the no. of terms of AP to be added to get the sum 72
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sn=n/2(2a+(n-1)d)
72=n/2(2*24+(n-1)-4)
144=48n+(n(n-1)-4)
144=48n+(n^2-n)-4
144=48n-4n^2+4n
144=52n-4n^2
36=13n-n^2
n^2-13n+36=0
n^2-9n-4n+36
n(n-9)-4(n-9)
(n-4)(n-9)
72=n/2(2*24+(n-1)-4)
144=48n+(n(n-1)-4)
144=48n+(n^2-n)-4
144=48n-4n^2+4n
144=52n-4n^2
36=13n-n^2
n^2-13n+36=0
n^2-9n-4n+36
n(n-9)-4(n-9)
(n-4)(n-9)
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