Question

what is the last term of AP 5/2,4, 11/2,7... if there are 20 term in the series​

Answer 1

Answer:hello jiminshi

Step-by-step explanation:It is known that, S  

n

​

=  

20

n

​

[2a+(n−1)d],

where n= number of terms , a= first term, and d= common difference

Here, a=−6,d=  

2

1

​

 

⇒−25=  

2

n

​

[2×(−6)+(n−1)(  

2

1

​

)]

⇒−50=n[−12+  

2

n

​

−  

2

1

​

]

⇒−50=n[−  

2

25

​

+  

2

n

​

]

⇒−100=n(−25+n)

⇒n  

2

−25n+100=0

⇒n  

2

−5n−20n+100=0

⇒n(n−5)−20(n−5)=0

⇒n=20  

⇒n=5