Which term of AP 5,9,13,17----------------is81

1.	Which term of AP 5,9,13,17----------------is81
Answer» The 20th term of given ap is 81 a=5 :d=9-5=4 :an=81 : n=..? an=a+(n-1)d81=5+(n-1)481-5=(n-1)476=(n-1)476/4= n-119 =n-119+1 =nn=20 a=5, d=9-5=4. an=81. an=a+(n-1)d. 81=5+(n-1)4. 81-5=(n-1)4. 76÷4=n-1. 19=n-1. 19+1=n. 20=n a = 5 , d = 9-5=4 , Tn=81 , n= ? AP of n th term is given by, Tn= a+ (n-1)d . Then, Tn = 5+(n-1)4 81= 5+4n-4 81+1=4n n= 82/4 n= 2.5 th term An=a+(n-1)d81=5+(n-1)481=5+4n-481=1+4n81-1=4n80=4n80/4=nN=20

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