Question

which of the following given us the value of seventeenth triangular number (a) 1+2+3+....+17 (b) 1+2+....+8 (c) 1+3+5+....+17 (d) 2+4+8+....+34

Answer 1

Step-by-step explanation:

sorry bro don't know answer

Answer 2

Answer:

By adding another row of dots and counting all the dots we can

find the next number of the sequence.

The first triangle has just one dot.

The second triangle has another row with 2 extra dots, making 1 + 2 = 3

The third triangle has another row with 3 extra dots, making 1 + 2 + 3 = 6

The fourth has 1 + 2 + 3 + 4 = 10

etc!

so, ans is

1,3,6,10,15,21..

We can use Xn to mean "dots in triangle n", so we get the rule:

Rule: Xn = n(n+1)/2

put n=17,

X17= 17*18/2=153.

we find 153 from option (a)

1+2+3+......+17

=17*18/2=153

so, option (A) ✅✅✅✅