Question

Calculate 1 - 2 + 3 - 4 5 - 6+ ...... + 179 - 180.
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Answer 1

Answer:

-90

Step-by-step explanation:

Given :

To find the value of :

1 - 2 + 3 - 4 + 5 - 6 + ... + 179 - 180

Solution :

1 - 2 + 3 - 4 + 5 - 6 + ... + 179 - 180  (totally 180 terms)

⇒ (1 - 2) + (3 - 4) + (5 - 6) + ... + (179 - 180)  (totally 90 terms)

⇒ (- 1) + (-1) + (-1) + ... + (-1)   ( 90 terms)

⇒ (-1) × 90 = -90

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