Question

If sn=n²+3n ,then find a20 and s20​

Answer 1

Answer:

n=37²

Step-by-step explanation:

If sn= n²+3n then find a20 and 20

3n²=20+20

3n²=40

n=3_40

n=37²

Answer 2

Answer:

a20=42 and s20 = 460

Step-by-step explanation:

$sn = {n}^{2} + 3n \\ s1 = {1}^{2} + 3 \times 1 = 4 \\ s2 = {2}^{2} + 3 \times 2 = 10 \\ a2 = s2 - s1 \\ = 10 - 4 = 6 \\ \\ d = a2 - a1 \\ = 6 - 4 = 2(s1 = a1) \\ \\ a20 = a + (n - 1)d \\ 4 + (20 - 1)2 \\ 4 + 19 \times 2 \\ 42 \\ \\ s20 = {n}^{2} + 3n \\ {20}^{2} + 3 \times 20 \\ 460$

Hope it helps.......

Mark it brainliest.......

Thank you......