When we add/subtract fractions, why do we need denominators?

Step-by-step explanation:

so we know what to add or subtract by

The real reason is due to the definition of the fraction itself, which is a representation of parts of a total which must be the same size. When you add or subtract fractions, you can't express the result as a fraction if you do not divide the total into equal parts.

a4 - 3a2 - 1

step-by-step explanation:

step   1   :

equation at the end of step   1   :

  ((a4) -   3a2) -   1

step   2   :

trying to factor by splitting the middle term

2.1     factoring   a4-3a2-1  

the first term is,   a4   its coefficient is   1 .

the middle term is,   -3a2   its coefficient is   -3 .

the last term, "the constant", is   -1  

i would say c is the best answer, hope it's right!

good luck! =)

cutie~