Question

in an a.p given a7=30 and a10= 42 find a and sn​

Answer 1

Step-by-step explanation:

a7=a+6d=30

a10=a+9d=42.

=>a+9d-a-6d=42-30

=>3d=12=>d=4

=>a+6(4)=30

=>a=6

Answer 2

Answer:

a = 6

Sn = 2n^2 + 4n

Step-by-step explanation:

a7 = 30

a + 6d = 30 ...........(i)

a10 = 42

a + 9d = 42 .............(ii)

Solving (i) and (ii)

-3d = -12

d = 4

putting d in (i)

a = 6

Sn = n/2 {2a + (n - 1)d}

= n/2 {12 + 4n - 4}

= n{4 + 2n}

Sn = 2n^2 + 4n

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