noun
telescoping series
Rare mathematical term for a series where partial sums cancel intermediate terms, leaving only the first and last.
望遠鏡級数は、部分分数分解を使って和を求めることが多い。
Telescoping series often use partial fraction decomposition to find the sum.
Compound of 望遠鏡 (telescope) and 級数 (series), from the way terms collapse like a folding telescope.