The fifth term of an ap is 1 and 11th term is -17.which term of ap is -77?
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given : a5= 1
a+4d =1. -1
a11 = -17
a+10d = -17. -2
subtracting eq 1 and 2
a+4d = 1
a+10d=-17
we get -6d = 18
d= -3
put value in eq1
a+4d=1
a+4×-3=1
a+(-12)=1
a= 1+12
a=13
an = a+(n-1)d
-77= 13 +(n-1)-3
-77-13= (n-1)×-3
-90 = (n-1) ×-3
-90/-3 =(n-1)
30 = (n-1)
30+1 =n
31=n
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