Question

The sum of the first 10 terms of an A.P. is 100 and the sum of the next 10 terms is 300. Find the sum of the first n terms of the A.P.

Answer 1

Answer:

Step-by-step explanation:that one was by mistake sry fr that

Answer 2

Here, given that...

The sum of first 10 terms of an A.P is 100...

i.e S10=100 and S10-- S20=300. We know that,

S =n/2[2a+(n–1)d]

i.e,, S20=20/2[2a+(20–1)d]

S20=10[2a+(19d)]=400 -------------{1}

Similarly.,

S10=10/2[2a+(10–1)d]

i.e,, S10=5[2a+(9d)]=100 ------------------{2}

By solving {1} and {2}, we have