Question

Plss solve......... IF THE SUM OF FIRST 7 TERMS OF AN AP IS 49 AND THAT OF FIRST 17 TERM IS 249 THEN FIND THE SUM OF FIRST N TERMS.

Answer 1

➡➡➡Using the formula
SUM = n/2 [ 2a+ (n-1)d]
So s7 = 49
So
A/Q
49 = 7/2 [ 2a + (7-1)d]
49*2/7 = 2a + 6d
14 = 2a + 6d
a +3d = 7 (1)

Now
s17 = 249
So
249 = 17/2 [ 2a ( 17-1)d]
289 * 2/17 = 2a + 16d
34 = 2a + 16d
a + 8d = 17(2)
a +3d = 7(1)
So

5d = 10
d = 2

And
a + 3*2 = 7
a = 1

So n terms

Sum = n/2 [ 2a + (n-1)d]
= n/2 [ 2*1 + (n-1)2]
= n/2 ( 2+ 2n -2)
= n/2 ( 2n)
n2

Hope it's right

Answer 2

Heya!!!

Your solution is in the attechment...
Hope it helps you ☺

Sorry for very late answer...
There was problem in uploading pic...