find the 20th term of AP whose 3rd term is 7 and seventh term exceed three time the 3rd term by 2. also find its nth term
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T3 = 7
=> a + 2d = 7 --------(1)
T7 - 3T3 = 2
=> a + 6d - 3(a+2d) = 2
=> a +6d - 3a - 6d = 2
=> - 2a = 2
=> a = - 1
On putting the value of a in equation 1, we get
-1 + 2 d = 7
=> 2d = 8
=> d = 4
T20 = a + 19d
= - 1+ 19 * 4
= - 1 + 76
= 75
= 75
Tn = a + (n-1)d
= - 1 + (n-1) 4
= - 1 +4n - 4
= 4n - 5
=> a + 2d = 7 --------(1)
T7 - 3T3 = 2
=> a + 6d - 3(a+2d) = 2
=> a +6d - 3a - 6d = 2
=> - 2a = 2
=> a = - 1
On putting the value of a in equation 1, we get
-1 + 2 d = 7
=> 2d = 8
=> d = 4
T20 = a + 19d
= - 1+ 19 * 4
= - 1 + 76
= 75
= 75
Tn = a + (n-1)d
= - 1 + (n-1) 4
= - 1 +4n - 4
= 4n - 5
Anonymous:
Correct !
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