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Question
Find a30 − a20 for the A.P.
−9, −14, −19, −24, ...
Solution
In this problem, we are given different A.P. and we need to find `a_30 - a_20`.
A.P. −9, −14, −19, −24, ...
Here
First term (a) = -9
Common difference of the A.P. (d) = - 14 - (-9)
= -14 + 9
= -5
Now as we know
`a_n = a + (n -1)d`
Here we find `a_30` and `a_20`
So for 30 th term
`a_30 = a + (20 - 1)d`
`= -9 + (19)(-5)`
= -9 - 95
= -104
So
`a_30 - a_20 = -154 - (-104)`
=-154 + 104
= -50
Therefore for the given A.P `a_30 - a_20 = -50`
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