Question

write the 10thand 15th tringlure number​

Answer 1

The 10thtriangular number is the 4thtriangular number plus 5 + 6 + 7 + 8 + 9 + 10. That is, 10 + 5 + 6 + 7 + 8 + 9 + 10. These can be added in order to give the 10th triangular number as 55.

Similarly, the 15tg trianglular no is 105.