12.3-12.5 · Series: arithmetic and geometric progressionsLesson 2 of 9Free preview
The sum of an arithmetic progression
Write the sum forwards and backwards. Each pair adds to a + l, so Sₙ = ½n(a + l) = ½n(2a + (n − 1)d).
12.3-12.5 · Series: arithmetic and geometric progressionsLesson 2 of 9Free preview
Write the sum forwards and backwards. Each pair adds to a + l, so Sₙ = ½n(a + l) = ½n(2a + (n − 1)d).