Janganlah ngasal wahai sahabat Poin 25​

nomor 2

pola segitiga —> Un = [n(n + 1)]/2

U₉₀ = [90(90 + 1)]/2

      = (90)(91)/2

      = (45)(91)

U₉₀ = 4.095

nomor 3

pola persegi panjang —> Un = n(n + 1)

U₅₁ = (51)(51 + 1)

     = (51)(52)

U₅₁ = 2.652

nomor 4

pola persegi —> Un = n²

U₁₇ = (17)²

U₁₇ = 289