Question

what is the sum of the first 20 terms and the last 20 terms of the sequence 6,10,14....​

Answer 1

Step-by-step explanation:

$\purple{ \clubs \sf \: Given : }$

• A.P. series is 6,10,14

$\purple{ \clubs \sf \:To \: find : }$

• Sum of first 20 terms.

$\purple{ \clubs \sf \: Formulas\: used\: :}$

$\sf \:S_n=n/2[2a+(n-1)d]$

$\purple{ \clubs \sf \: Solution\: :}$

• First term (a) = 6
• Difference (d) = $\sf \: a_2 - a_1 \\ \sf \: 10 - 6 \\ \sf \: 4$
• Number of terms (n) = 20

$\sf \:S_{20}=20/2[2 \times 6+(20-1)4]$

$\sf \:S_{20}=10[12+(19)4]$

$\sf \:S_{20}=10[12+76]$

$\sf \:S_{20}=10 \times 88$

$\sf \:S_{20}=880$