Question

PLZ ANSWER FAST
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find the sum of first 30 terms of an A-P whose second term is 2
and sevenh term is 22
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Answer 1

Answer:

1680

Step-by-step explanation:

Let a is first term and d is common difference.

nth term = a + (n-1)d

=> 2nd term = 2

=> a + d = 2

=> a = 2 - d ---:1

=> 7th term = 22

=> a + 6d = 22

Put a = 2 - d from eq. 1

=> 2 - d + 6d = 22

=> 2 + 5d = 22

=> 5d = 22-2= 20

=> d = 20/5= 4

So,

a = 2 - 4 = - 2

Sum = $\dfrac{n}{2}(2a+(n-1)d)$

Sum = $\dfrac{30}{2}(2(-2)+(30-1)(4))$

Sum = 15( - 4 + 116)

Sum = 1680