Question

Given the polynomial 21x^4+3y-6x^2+34 1. What polynomial must be subtracted from it to obtain 29x^2-7? 2. What polynomial must be added to it to obtain a first degree polynomial?

Answer 1

`21x^4+3y-35x^2+41` must be subtracted

As you can see, we added -x+2 to this polynomial to obtain a first degree polynomial. (Though really anything with an x would do. For example, 3x, 2221x, or -224x would all work)

Explanation:

We have the following polynomial

`21x^4+3y-6x^2+34`

And need to find a polynomial to subtract from it to get

`29x^2-7`

This means that if we subtract these two polynomials, we will get our desired polynomial

`21x^4+3y-6x^2+34-(29x^2-7)\\\\21x^4+3y-6x^2+34-29x^2+7\\\\21x^4+3y-35x^2+41`

Just to be sure, we can then check our work by finding the difference of the first polynomial and the one that we just found

`21x^4+3y-6x^2+34-(21x^4+3y-35x^2+41)\\\\21x^4+3y-6x^2+34-21x^4-3y+35x^2-41\\\\-6x^2+34+35x^2-41\\\\29x^2-7`

As we got the desired result, we know that this answer is correct.

And now for the second part of the problem. What polynomial must be added to it to obtain a first degree polynomial?

Recall that a first degree polynomial is one that has the total sum of 1. For example the polynomial x+5 is a first degree polynomial, but x+y+5 has a degree of 2.

This means that our desired polynomial needs to only have some amount of x's and constants.

We can do the same thing as the first time and simply subtract our desired result from the first polynomial. For simplicity, let us use the simple polynomial x+2

`21x^4+3y-6x^2+34-(x-2)\\\\21x^4+3y-6x^2+34-x+2\\\\21x^4+3y-6x^2-x+36`

As you can see, we added -x+2 to this polynomial to obtain a first degree polynomial. (Though really anything with an x would do. For example, 3x, 2221x, or -224x would all work)