Question

find the fourteenth and fifteenth triangular numbers and find their sum verify the statement 8 for this sum

Answer 1

fourteenth triangular numbers = n(n+1)/2

here n=14

then n = 14(14+1)/2

n=14(15)/2

n=7*15

n=105

Fifteenth triangular numbers = n(n+1)/2

here n=15

n=15(15+1)/2

n=15(16)/2

n=15*8

n=120