Quant Question Of The Day: 41
[latexpage]
Functions
Let f(x) is a polynomial such that f(f(x)) –x2 =xf(x),then what is the value of f(-91)?
1. 90
2. -92
3. 0
4. Cannot be determined
Let’s suppose that degree of the given polynomial f(x) = n then degree of the polynomial f(f(x)) will be n2 and degree of xf(x) is n+1.
f(f(x)) = xf(x)+x2
Equating degrees of polynomials on both sides, we get that for any positive value of x, there is no such polynomial is possible if degree of polynomial is greater than 1.
Means f(x) is a linear equation
i.e. f(x) = –(x+1)
Or, f(-91) = 90
Solve our previous ‘questions of the day’
Quant Question Of The Day: 40
Quant Question Of The Day: 39
0
1. 90
Sir
I suppose it should be 90 instead of -92 as if we substitue value of x= -91 in the equation f(x)= -(x+1), we get f(-91) = 90