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