4x^(3) - 16x^(2) - 20x factor completely. explain what goes on in the equation?

Question

4x^(3) - 16x^(2) - 20x  factor completely. explain what goes on in the equation?

campbell_st · Answer

take out the common factor of 4x

4x(x^2 - 4x - 5) 

all you need to do now is factorise the quadratic

jhonyy9 · Answer

x^2 -4x -5 how can you factorize it ?

aimmebgood · Answer

i dont know.

campbell_st · Answer

ok... you need 2 factors of - 5 that add to - 4

5 is prime so you are using the factors 1 and 5 to get - 4

campbell_st · Answer

any ideas

aimmebgood · Answer

-5 + 1 ?

campbell_st · Answer

ok so you will have 

4x(x - 5)(x + 1)

all done

aimmebgood · Answer

but where does the -5 and the +1 come from in the equation?

campbell_st · Answer

ok... if are you happy with taking 4x as a common factor to get

4x(x^2 - 4x - 5)

the quadratic can be written as 

4x(x^2 +x - 5x - 5)

aimmebgood · Answer

thanks. that was more simple than i thought.