Question

calculate 1-2+3-...............+179-180 please answer with solution

Answer 1

use formula (n/2)(2a +(n-1)d)

Answer 2

S =   1 - 2 + 3 - 4 + 5 - 6 + ___ + 179 - 180

+   S =       1 - 2 + 3 -  4 + 5 - 6 + ___ + 179 - 180

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2S =           1 - 1 - 1 - 1 - 1 - 1 - 1 - 1 - ___ - 1 - 1 - 1 - 180

2S = -180  

S =  $\frac{-180}{2}$

S = -90