Question

in an A.P the first term is 22 ,the common difference is -4, and sum of n terms is 64 ,find n?​

Answer 1

Answer:

4 and 8.

Step-by-step explanation:

First term = a =22.

Common Difference = d = -4.

Sum of n terms = Sₙ = 64.

Number Of Terms = n = ?.

Sₙ = n/2 × [ 2a + (n - 1)d ]

64 = n/2 × [ 2 × 22 + (n - 1) × (-4) ]

There will be a quadratic equation for n.

After Solving the above equation, we get.

4n² -  48n = 128.

On Solving this we get,

.

n = 4 and 8.

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