Question

in an ap :(v) given d=5, S9 = 75. find a and a9

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Answer 1

Answer:

a = -35/3 and a9 = -85/3

Step-by-step explanation:

Given: d=5,s9 =75

we have, Sum = n/2 [2a + (n-1) d]

putting the values in formula

s9 = 9/2 [2a+(9−1)5]

75 = 9/2[2a+40]

150 = 9 [2a+40]

150 = 18a+360

150−360 = 18a

−210 = 18a

-210/18 = a

a= −35/3

Now

we have, a (for nth term) = a + (n-1) d

putting the values in formula

a9 = a+(9−1)5

a9 = −35/3 + 40

a9 = (−35 + 120) /3

a9 = -85/3

Hence, a = -35/3 and a9 = -85/3

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