Wednesday, December 30, 2015

find the real, linear, quadratic and irreducible factors of x^5 - 32

x^5-32. We have to factorise
this.


Solution:


Let f(x) =
x^5- 32.


Put x= 2  in f(x) = x^5-
32.


f(2) = 2^5 - 32 = 32-32 =
0.


So by remainder theorem, (x-2) is a factor of
x^5-32.


We know that (x^n-a^n)/(x-a) = x^(n-1) -
ax^(n-2)++a^2*x^(n-3)+a^3*x^(n-4)+....+a^(n-2)*x +a^n is an identity.Therefore (x^n-a^n)
= (x-a) {x^(n-1) - ax^(n-2)++a^2*x^(n-3)+a^3*x^(n-4)+....+a^(n-2)*x
+a^n}


We use the above to factor  f(x) = x^5 - 32 = x^5 -
2^5..


Therefore  x^45 - 2^5 = (x-2){
x^4+2x^3+2^2*x^2+2^3x+2^4}.


x^5- 32 =
(x-2)(x^4+2x^3+4x^2+8x+16).


So x-2 is the linear
factor.


So x^5 - 32 =
(x-2)(x^4+2x^3+4x^2+8x+16).

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