Use Factor Theorem to verify that x + a is a factor of xn + an for any odd positive integer n.

Let p(x) = xn + an
The zero of x + a is - a. | x + a = 0 ⇒ x = - a
Now,
p(- a) = (- a)n + an = (- 1)nan + an
         = (- 1)an + an 
    
because n is an odd positive interger
therefore   (-1)n = - 1
= - an + a= 0
∴ By Factor Theorem, x + a is a factor of xn + an for any odd positive integer n.

363 Views

Advertisement

Without actual division prove that x4 + 2x3 - 2x2 + 2x - 3 is exactly divisible by x2 + 2x - 3. 


x2 + 2x - 3
= x2 + 3x - x - 3
= x(x + 3) - 1 (x + 3)
= (x + 3) (x - 1)
Let p(x) = x4 + 2x3 - 2x2 + 2x - 3
We see that
p(-3) = (-3)4 + 2(-3)3 - 2(-3)+ 2(-3) - 3
= 81 - 54 - 18 - 6 - 3
= 0
Hence by converse of factor theorem, (x + 3) is a factor of p(x).
Also, we see that
p(1) = (1)4 + 2(1)3 - 2(1)2 + 2(1) - 3
= 0
Hence by converse of factor theorem, (x - 1) is a factor of p(x).
From above, we see that
(x + 3) (x - 1), i.e., x2 + 2x - 3 is a factor of p(x)
⇒ p(x) is exactly divisible by (x2 + 2x - 3).

407 Views

Advertisement
Determine the value of ‘b’ for which the polynomial 5x3 - x2 + 4x + b is divisible by 1 - 5x.

Let p(x) = 5x3 - x2 + 4x + b
1 - 5x = 0

rightwards double arrow space space space space space space space space 5 straight x space equals space 1 space space space rightwards double arrow space space space straight x space equals space 1 fifth

therefore  The zero of 1 - 5x is 1 fifth
If p(x) is divisivle by 1 - 5x, then straight p open parentheses 1 fifth close parentheses equals 0
                                         | By Factor Theorem
rightwards double arrow space 5 open parentheses 1 fifth close parentheses cubed minus open parentheses 1 fifth close parentheses squared plus 4 open parentheses 1 fifth close parentheses plus straight b equals 0
rightwards double arrow space space 1 over 25 minus 1 over 25 plus 4 over 5 plus straight b equals 0
rightwards double arrow space space space 4 over 5 plus straight b equals 0
rightwards double arrow space space space space straight b space equals space minus 4 over 5.

582 Views

For what value of a the polynomial 2x3 + ax2 + 11x + a + 3 is exactly divisible by 2x - 1?

Let p(x) = 2x3 + ax2 + 11x + a + 3
If p(x) is exactly divisible by 2x - 1, then by factor theorem,

space space space space space space straight P open parentheses 1 half close parentheses equals 0 space space space space 12 straight x minus 1 equals 0 space rightwards double arrow space straight x space equals space 1 half
rightwards double arrow space space space 2 open parentheses 1 half close parentheses cubed plus straight a open parentheses 1 half close parentheses squared plus 11 open parentheses 1 half close parentheses plus straight a plus 3 equals 0
rightwards double arrow space space space 1 fourth plus straight a over 4 plus 11 over 2 plus straight a plus 3 equals 0
rightwards double arrow space space space space fraction numerator 5 straight a over denominator 4 end fraction plus 35 over 4 equals 0
rightwards double arrow space space space space space straight a space equals space minus 7

Hence, the required polynomial is
2x3 - 7x2 + 11x - 7 + 3
or 2x3 - 7x2 + 11x - 4

262 Views

Find the values of a and b so that (x + 1) and (x - 1) are factors of x4 + ax3 - 3x2 + 2x + b.  

Let p (x) = x4 + ax3 - 3x2 + 2x + b
If (x + 1) and (x - 1) are factors of p(x), then by factor theorem,
p(-1) = 0 ...(1) | x + 1 = 0 ⇒ x = -1
and    p(1) = 0 ...(2) | x - 1 = 0 ⇒ x = 1
Now,
P(-1) = 0
⇒ (-1)4 + a(-1)3 - 3(-1)2 + 2 (-1) + b = 0
⇒ 1 - a - 3 - 2 + b = 0
⇒    -a + b = 4    ...(3)
and    p(1) = 0
⇒ (1)4 + a(1)3 - 3(1)2 + 2 (1) + b = 0
⇒ 1 + a - 3 + 2 + b = 0
⇒    a + b = 0    ...(4)
Solving (3) and (4), we get
a = -2,b = 2

183 Views

Advertisement