Question

a = 2
d = 7
an=72
n=?
Sn=?
​

Answer 1

Answer:

An =a+(n-1)d

Step-by-step explanation:

72 =2+(n-1)7

72 =2+ 7n - 7

72-2 =7n-7

70 =7n - 7

70+7 =7n

77 =7n

77/7=n

N=11

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Answer 2

Step-by-step explanation:

a=2

d=7

An=72

n=?

Sn=?

to find (n):-

An=a+(n-1)×d

72=2+(n-1)×7

72=2+7n-7

72= -5+7n

72+5=7n

77=7n

77/7=n

11=n

to find Sn :-

Sn=n/2(2a[n-1]×d)

Sn=11/2(2×2[11-1]×7)

Sn=11/2(4[10]×7)

Sn=11/2(4+70)

Sn=11/2(74)

Sn=11/2×(74)

now we will cut(divide)74 from 2and we will got 37

so,11×37=407

Sn=407