Question

please guys answer it is very urgent...
Q. 12 please​

Answer 1

Answer:

a) 10 will be the right answer..

Now,

Sn =210

a=3

d=7-3

=4

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

210 = n/2 [ 2*3 + (n-1) 4]

210 = n/2 [6 + 4n - 4]

210 = n/2 * 2 [1 + 2n]

210 = n [1+2n]

210 = n + 2n²

2n² + n - 210 =0

2n² +(21-20)n - 210 =0

2n² + 21n - 20n - 210 =0

n(2n + 21) - 10(2n + 21)=0

(2n + 21) (n - 10 ) =0

n = -21/2. ( not accepted ) & n= 10

So the answer will be 10 ..

hope u get your answer...

Answer 2

Step-by-step explanation:

a=3

d=7-3=4

the last term is 210

Number of terms =?

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