Question

solve this please .....BCB

Answer 1

Answer:

s=200

ap series=20,19,18

d=19-20=-1

a=20

an=?

n=?

an=a+(n-1)d

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

200=n/2(2*20+(n-1)-1)

200=n/2(40 -1n+1)

400=n(39-n)

400=39n-n square

now u can solve this equation and then u get the value of n and u can find an by the formula