Question

plz tell me answer find n​

Answer 1

Answer:

a1=12

a2=16

a3=20

d=4

sn=n/2(2a+(n-1)d)

672×2=n(2×12+(n-1)4)

1344=24n+4n^2-4n

1344=20n+4n^2

1344/4=5n+n^2

336=n^2+5n

n^2+5n-336=0

after solve this equation

we get

n=16,-21

then n is 16

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