Question

if the sum of first 14terms of an A.P is 1050 and it's first term is 10 then find the common difference​

Answer 1

Answer:

ANSWER

S

14

=1050

a=10

S

n

=

2

n

[2a+(n−1)d]

1050=

2

14

[2×10+(14−1)d]

7

1050

=[20+14d−d]

150−20=13d

130=13d

d=10

The 20

th

term is

a

20

=a+(n−1)d

=10+(20−1)10

⇒10+190

a

20

⇒200

Answer 2

a=10

d=? n= 14

Sn=1050

using formula

$s = \frac{n}{2} (2a + (n - 1)d)$

$1050= \frac{14}{2} (2 \times 10 + (14 - 1)d)$

$1050 = 7(20 + (13)d)$

$1050 = 140 + 91d$

$1050 - 140 = 91d$

$910 = 91d$

$\frac{910}{91} = d$

$d = 10$