Question

an=4, d = 2 और Sn =-14 दिया है। n और a ज्ञात कीजिए।​

Answer 1

Answer:

• The required values of n and a are 7 and -8 respectively.

Step-by-step explanation:

We have been given the following points:

• An (Last term) = 4
• d ( Common difference) = 2
• Sn ( Summation of AP) = -14

We have to find the value of n and a of the AP.

• Here, We will use the formula of AP which is given below.
• An = a + (n-1)d
• 4 = a + (n -1)2
• 4 = a + 2n - 2
• 6 = a + 2n
• a = 6 - 2n .... (I)

Now, we will use summation formula of AP.

• Sn = n/2[2a + (n-1)d]

-14 = n/2[2(6 - 2n) + ( n -1)2

-14 = n/2[12 - 4n + 2n - 2]

-14 = n/2[10 - 2n]

-14 = n/2[10 - 2n]

-28 = 10n - 2n²

2n² - 10n - 28 = 0

2(n² - 5n - 14) = 0

n² - 5n - 14 = 0

(n + 2)(n - 7) = 0

We will take value in positive, so we will have to neglect the negative value. I.e (n = - 2)

• The required value of n will be 7.

Putting value of n in equation (I) :

• a = 6 - 2n
• a = 6 - 2(7)
• a = 6 - 14
• a = -8

Therefore, the required value of a is -8.

Answer 2

Solution is attached here