Find the sum of 20 terms of the series

1^{2 }- 2^{2 }+ 3^{2 }- 4^{2 }+ 5^{2 }- 6^{2 }+ ........ 20 terms.

**calculate 1 ^{2}-2^{2}, 3^{2}-4^{2},.....19^{2}-20^{2}**

**we will get an AP=>-3,-7,-11,....-39**

**a=-3**

**d=-4**

**a _{n}=-39**

**find n and then s _{n}**

**if u are satisfied, thumbs up pleaseeee....**

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