JEE MAIN - Mathematics (2021 - 18th March Evening Shift - No. 16)
If f(x) and g(x) are two polynomials such that the polynomial P(x) = f(x3) + x g(x3) is divisible by x2 + x + 1, then P(1) is equal to ___________.
Answer
0
Explanation
Given, p(x) = f(x3) + xg(x3)
We know, x2 + x + 1 = (x $$-$$ $$\omega$$) (x $$-$$ $$\omega$$2)
Given, p(x) is divisible by x2 + x + 1. So, roots of p(x) is $$\omega$$ and $$\omega$$2.
As root satisfy the equation,
So, put x = $$\omega$$
p($$\omega$$) = f($$\omega$$3) + $$\omega$$g($$\omega$$3) = 0
= f(1) + $$\omega$$g(1) = 0 [$$\omega$$3 = 1]
= f(1) + $$\left( { - {1 \over 2} + {{i\sqrt 3 } \over 2}} \right)$$ g(1) = 0
$$ \Rightarrow $$ f(1) $$-$$ $${{g(1)} \over 2} + i\left( {{{\sqrt 3 g(1)} \over 2}} \right)$$ = 0 + i0
Comparing both sides, we get
f(1) $$-$$ $${{g(1)} \over 2}$$ = 0
and $${{{\sqrt 3 } \over 2}g(1) = 0}$$ $$ \Rightarrow $$ g(1) = 0
So, f(1) = 0
Now, p(1) = f(1) + 1 . g(1) = 0 + 0 = 0
We know, x2 + x + 1 = (x $$-$$ $$\omega$$) (x $$-$$ $$\omega$$2)
Given, p(x) is divisible by x2 + x + 1. So, roots of p(x) is $$\omega$$ and $$\omega$$2.
As root satisfy the equation,
So, put x = $$\omega$$
p($$\omega$$) = f($$\omega$$3) + $$\omega$$g($$\omega$$3) = 0
= f(1) + $$\omega$$g(1) = 0 [$$\omega$$3 = 1]
= f(1) + $$\left( { - {1 \over 2} + {{i\sqrt 3 } \over 2}} \right)$$ g(1) = 0
$$ \Rightarrow $$ f(1) $$-$$ $${{g(1)} \over 2} + i\left( {{{\sqrt 3 g(1)} \over 2}} \right)$$ = 0 + i0
Comparing both sides, we get
f(1) $$-$$ $${{g(1)} \over 2}$$ = 0
and $${{{\sqrt 3 } \over 2}g(1) = 0}$$ $$ \Rightarrow $$ g(1) = 0
So, f(1) = 0
Now, p(1) = f(1) + 1 . g(1) = 0 + 0 = 0
Comments (0)
