Question

1) Solve : 1+5 +9 +... +x = 1770 Hints :
(1) The given sequence is an A.P. (2) Write the value of a and d.
(3) Sn = 1770.
(4) Use the formula and get a quadratic equation and find the value of n.
(5) The nth term is x.
(6) Use formula : Sn=n/2(a+l)
(7) Find the value of x.
Ans. x=117.​

Answer 1

Answer:

Step-by-step explanation:At first u will get a and d

1+5+9+...+x

The first term = a

So a=1

d is the common difference.So,

d=9-5=4

l=a+(n-l) d

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

Then u substitute

Sn=1770 a=1 d=4

1770=(n/2)[2(1)+(n-1) 4]

1770=(n/2)[2+4n-4]

Multiply thru by 2 to remove the 'divided by two!

1770(2)=n(2+4n-4)

3540=2n+4n^2-4n

3540=4n^2-2n

Then make it a quadratic equation

4n^2-2n-3540

Now factorise