non applicability of master theorem

Question

in which of the following recurrence relation master theorem can not be applied and why

a)T(n)=7T(n/2)+n^2

b)T(n)=7T(n/3)+n^2

c)T(n)=T(9n/10)+n

d)T(n)=T(n-1)+n

Answer 1

Clearly we can aplly master thoerm in form of T(n) = a T(n/b) + f(n).

D is not in this form.

Comments

but we have to also check that either f(n) or o(n^{logb a}) is asymptotocally larger or polynomially larger na ? 

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First requirment to apply master thoerm is  it will be in form of  T(n) = a T(n/b) + f(n) where a>0 and b>1 not satify by format of 4rth option.