what does the sigma notation look like for the sequence 1/4,-1/9,1/16,-1/25

Answer 1

The denominator is i², so the term is 1/i².
The signs are alternating, so multiply each term by (-1)^i to get

5
∑ (-1)^i / i²
i=2

Answer 2

Nowadays, students are very likely to avoid STEM, especially math. Students should take math from school level so that they don't have to face any problem in future. Schools also should take the matter seriously. Unfortunately most of the public schools do not do so.