Question

The 14th term of an AP
is twice the 8th term.if the 6th term is -8 then find tge sum of first 20 terms

Answer 1

Answer:

=a14=2*a8(given)

=a+13d=2(a+7d)

=a+13d=2a+14d

=a+d=0

=a=-d

a6=a+5d= -8(given)

a6=-d+5d=-8(a=-d)

=4d=-8

=d=-2

=a=-d=-(-2)

=a=2

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

S20=20/2(2*2+(20-1)(-2)

=10(4+19(-2))

=10(4-38)

=10*-34

=-340