Question

-25= ņ/2 [-12+(n-1) 1/2]
Arithematic. Progression
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Answer 1

Answer:

-50=n (-12 + n/2 -1/2)

50=n (-12- 1/2 + n/2)

50=n (-25/2+ n/2 )

100=-25n + n^2

n^2-25n-100

then make factores u will get your answer.