Question

find the sum of first 4 terms in the A.P where a=5,d=–5 with out using any formula ​

Answer 1

Answer:

$\large\boxed{\sf{-25}}$

Step-by-step explanation:

For an A.P, given that,

• First term , a = 5
• Common difference, d = - 5

Therefore, second term = a + d

=> Second term = 5 - 5

=> Second term = 0

Therefore, third term = a + 2d

=> Third term = 5 +2(-5)

=> Third term = 5 - 10

=> Third term = -5

Therefore, fourth term = a + 3d

=> Fourth term = 5 + 3(-5)

=> Fourth term = 5 -15

=> Fourth term = -10

Therefore, fifth term = a + 4d

=> Fifth term = 5 + 4(-5)

=> Fifth term = 5 -20

=> Fifth term = -15

Therefore, sum of five terms

= 5 + 0 + (-5) + (-10) + (-15)

= 5 - 5 - 10 - 15

= 0 - 10 - 15

= -10 - 15

= - (10 + 15)

= - 25

Hence, required sum of five terms = -25

Answer 2

Answer:

-10 is the answer.

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Step-by-step explanation:

Given:

first term (a)= 5

common difference (d)= -5

no. of terms (n)= 4

$Sn = \frac{n}{2}(2a + (n - 1)d) \\ = > \frac{4}{2}(2 \times 5 + ( 4 - 1) - 5) \\ = > 2(10 + (3) - 5) \\ = > 2(10 - 15) \\ = > 2( - 5) \\ = > - 10$

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hope it helps uh!!