Question

FIND THE VALUE OF x...

FIND THE X ​

Answer 1

Answer:

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Step-by-step explanation:

Here, a=1 and d=3. 

Let it contain n terms. 

As we know, the sum of n terms of an A.P. 

Sn=2n×[2a+(n−1)d]

Then,

2n⋅[2a+(n−1)d]=715

⇒2n⋅[2×1+(n−1)×3]=715

⇒n(3n−1)=1430

⇒3n2−n−1430=0

⇒3n2−66n+65n−1430=0

⇒3n(n−22)+65(n−22)=0

⇒(n−22)(3n+65)=0

⇒n=22

∴x=T22=(a+21d)=(1+21×3)=64.

Answer 2

Answer:

64

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