Question

21. The first of an AP is 5. the last te is 45 and the sun is 400. Find the number of terms and the common difference​

Answer 1

Answer:

16

Step-by-step explanation:

a=5

An=45

Sn=400

Sn=n/2(a+L). (L=An)

400=n/2(45+5)

400=n/2*50

400=25n

n = 16

Answer 2

Answer:

d=8/3, n=16 terms

Step-by-step explanation:

given a= 5

Tn=45

Tn=a+(n-1)d.....eqn1

Sn=n/2(a+Tn)

400=n/2(5+45)

400=n/2(50)

400=n(25)

n=16 terms.....eqn2

substitute eqn 2 in eqn 1

45=5+(16-1)d

45=5+15d

40=15d

d=40/15

d=8/3

hope you understand

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