Question

The first term of an A.P. is – 5 and the 6th term is 45. Find S6​​

Answer 1

Answer:

120

Step-by-step explanation:

Given that :

a = -5, T6 = 45

As we know that :

Tn = a + (n – 1)d

=> T6 = -5 + (6 – 1)d

=> 45 = -5 + 5d

=> 5d = 45 + 5

=> 5d = 50

=> d = 10

Also we know that :

Sn = n/2[ 2a + (n – 1)d ]

=> S6 = 6/2[ 2×(-5) + (6-1)10 ]

=> S6 = 3[ -10 + 50 ]

=> S6 = 3 × 40 = 120

Answer 2

Answer:

as 6th term is 45

a+5d=45

-5+5d=45

d=10

S6=n/2(2a+(n-1)d)

=6/2(2(-5)+(6-1)10)

=3(-10+50)

=3(40)

=120