Question

Given f(x) = x * f(x-1) for any natural number'x'. If f(x+2) = 20 * f(x),then what is the value of x?
a) 2
b) 4
c) 5
d) None of these​

Answer 1

Answer:

x=3 or -6

Thus option (d) is correct

Step-by-step explanation:

f(x) = x * f(x-1)

So f(x+2)=(x+2) f(x+1)

f(x+2)=(x+2)(x+1)f(x).......................(1)

f(x+2) = 20 * f(x)..............................(2)

THus (x+2)(x+1)f(x).=20*f(x)

So (x+2)(x+1)=20

x²+3x-18=0

(x+6)(x-3)=0

x=3 or -6

Thus option (d) is correct