Let f: R R be such that f(xy)=f(x)f(y), for all x, y R and f(0) 0. Let g: [1, ) R be a differentiable function such that x2g(x)= 1x (t2f(t)-tg(t) )dt. Then g(2) is equal to :
- 138
- 1116
- 1532
- 1764
Answer
(3) 1532
Solution
Put x=y=0: f(0)=f(0)2; f(0) 0 f(0)=1
Put y=0: f(0)=f(x)f(0) f(x)=1 for all x
x2g(x)= 1x (t2-tg(t) )dt ...(i)
Put x=1 in (i): g(1)=0
Differentiate (i) with respect to x:
2xg(x)+x2g'(x)=x2-xg(x)
g'(x)+ 3xg(x)=1 (linear differential equation)
I.F. =e 3xdx=x3
x3g(x)= x3dx= x44+C
g(1)=0 C=- 14 g(x)= x4-14x3
g(2)= 16-132= 1532
Answer: (3)