Question

sn=n/2[2a+(n-1) d, sn=48 , d=-4, a=20, find n​

Answer 1

Answer:

i am chinese don't understand the language sorry

Answer 2

Answer:

Given, a=5,d=3,an=50

⇒a+(n−1)d=50

⇒5+(n−1)3=50

⇒5+3n−3=50⇒3n=48⇒n=16

∴S16=216[2a+(16−1)d]=8[2×5+15×3]=440

Hence, n=16,S16=440