Question

Fill in the blanks : the the sum of the AP, 1+2+3+4+5+6 ...…15 , Find the sum is​

Answer 1

Answer:

120

Sn=n/2(a+an)

=15/2(1+15)

=15/2(16)

=15x8

=120

Answer 2

Answer:

• The sum of the AP - 1 + 2 + 3 + 4 + ... + 15 is 120

Solution:

Here,

→ First Term (a) = 1

→ Common Difference (d) = 1

→ Total number of terms = 15

We know that,

→ Sum of first n terms = n/2[2a + (n - 1)d]

So,

→ Sum = 15/2 × (2 × 1 + (15 - 1) × 1]

→ Sum = 15/2 × (2 + 14)

→ Sum = 15/2 × 16

→ Sum = 15 × 8

→ Sum = 120

• So, the sum first 15 terms of this AP is 120.