NCERT Solutions
Class 9 Maths
Polynomials

Ex.2.4 Q.1
Determine which of the following polynomials has (x + 1) a factor:
(1) x3 + x2 + x + 1
(2) x4 + x3 + x2 + x + 1
(3) x4 + 3x3 + 3x2 + x + 1
(4) x3 – x2 – (2 + √2) x + √2
(1) For x + 1 = 0, we have x = –1
Now, p (–1) = (–1)3 + (–1)2 + (–1) + 1
= –1 + 1 – 1 + 1
= 0
i.e., when p(x) is divided by (x + 1), then the remainder is zero.
So, (x + 1) is a factor of x3 + x2 + x + 1.
(2) For x + 1 = 0, we have x = –1.
Now, p (–1) = (–1)4 + (–1)3 + (–1)2 + (–1) + 1
= 1 –1 + 1 – 1 + 1
= 1
i.e., when p(x) is divided by (x + 1), then the remainder is zero.
Since p(x) is not divisible by x + 1
Hence, (x + 1) is not a factor of x4 + x3 + x2 + x + 1.
(3) For x + 1 = 0, we have x = –1.
Now, p (–1) = (–1)4 + 3(–1)3 + 3(–1)2 + (-1) + 1
= 1 – 3 + 3 – 1 + 1
= 1
i.e., when p(x) is divided by (x + 1), then the remainder is zero.
Since p(x) is not divisible by x + 1.
Hence, (x + 1) is not a factor of x4 + 3x3 + 3x2 + x + 1.
(4) x3 – x2 – (2 + √2) x + √2
For x + 1 = 0, we have x = –1.
Now, p (–1) = (-1)3 – (-1)2 – (2 + √2) (-1) + √2
= –1 - 1 + (2 + √2) + √2
= 2√2
i.e., when p(x) is divided by (x + 1), then the remainder is zero.
Since p(x) is not divisible by x + 1
So, (x + 1) is not a factor of x3 – x2 – (2 + √2) x + √2.