If c>0, 4a+cthe root of the equation f(x)=ax^2 -bx +c=0,lie in which interval.

That depends on the options provided.

Or U need to tell more. this data is insufficient.

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At this point it is given that c is positive and f(2) is less than 0.

Hence, the graph would be passing through the intecept c and a would be obvious negative as from 4a + c – 2b  is less than 0 given and thus the graph would be facing downlwards.

Hence the inetrval should be if nothing is given would be,

(-infinity,2)