Question

if ap series is 1,3,5,7...... find the sum of 10th term​

Answer 1

So as we can see every equation is formed by this formula:

i*i+1

So let's find the 10 number:

1 number=0*0+1

=1

2 number=1*1+1

=3

3 number=2*2+1

=5

4 number=3*3+1

=7

5 number=4*4+1

=9

6 number=5*5+1

=11

7 number=6*6+1

=13

8 number=7*7+1

=15

9 number=8*8+1

=17

10 number=9*9+1= 19

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hope it helps!

✨

Answer 2

Given:

• First term = a = 1
• Common Difference = d = 3 - 1 = 2

To find:

⟶ Sum of 10 terms = S₁₀ = ?

Method:

$\sf{S_n = \dfrac{n}{2} \times (2a + (n - 1)d)}\\\\\\\\\longrightarrow \: \sf{S_{10} = \dfrac{10}{2} \times (2(1) + (10-1)\times 2)}\\\\\\\longrightarrow \: \sf{S_{10} = 5 \times (2 + 9(2))}\\\\\\\longrightarrow \: \sf{S_{10} = 5 \times (2 + 18)}\\\\\\\longrightarrow \: \sf{S_{10} = 5 \times (20)}\\\\\\\therefore \: \large{\bf{\boxed{\bf{S_{10} = 100}}}}$

Other useful formula:

1. aₙ = a + (n - 1)d
2. Sₙ = n/2 (First term + Last term)