Question

plzz it's very urgent do fast plzz

Answer 1

1)The 8th triangular number is 36
The 9th triangular number is 45

Hence, their sum=36+45= 81

Clearly 81. is square of 9.

2)The 13th triangular number is 91
The 14th triangular number is 105

Hence, their sum=91+105=196

Clearly 196 is square of 14

Answer 2

1.

For 8 th = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 = 36

For 9th = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45

Now add both 36 and 45 = 36 + 45 = 81

Its square number of 9

2.

for 13 = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 = 91

For 14 =  1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 = 105

Now add both = 91 + 105 = 196

Its square number of 14