Question

in an A.P. if S21=1250, S20=1200,find a21​

Answer 1

Answer:

Formula

(a+b)

2

=a

2

+b

2

+2ab

=>a

2

+b

2

=(a+b)

2

−2ab

Given, a+b=5 and ab=6

So, a

2

+b

2

=(a+b)

2

−2ab=5

2

−2×6=25−12=13