College

Which equation can be solved by using this system of equations?

[tex]
\[
\begin{cases}
y = 3x^3 - 7x^2 + 5 \\
y = 7x^4 + 2x
\end{cases}
\]

[/tex]

A. [tex]\(3x^3 - 7x^2 + 5 = 0\)[/tex]

B. [tex]\(3x^3 - 7x^2 + 5 = 7x^4 + 2x\)[/tex]

C. [tex]\(7x^4 + 2x = 0\)[/tex]

D. [tex]\(7x^4 + 3x^3 - 7x^2 + 2x + 5 = 0\)[/tex]

Answer :

We start with the system

[tex]$$
\begin{cases}
y = 3x^3 - 7x^2 + 5, \\
y = 7x^4 + 2x.
\end{cases}
$$[/tex]

Since both equations equal [tex]$y$[/tex], the intersection points occur when

[tex]$$
3x^3 - 7x^2 + 5 = 7x^4 + 2x.
$$[/tex]

This is the equation from which we need to solve for [tex]$x$[/tex]. Therefore, the correct choice is the equation

[tex]$$
3x^3 - 7x^2 + 5 = 7x^4 + 2x.
$$[/tex]

This corresponds to option 2.

For completeness, if we were to rearrange the equation, we subtract [tex]$7x^4 + 2x$[/tex] from both sides to obtain

[tex]$$
3x^3 - 7x^2 + 5 - 7x^4 - 2x = 0.
$$[/tex]

Reordering the terms gives

[tex]$$
-7x^4 + 3x^3 - 7x^2 - 2x + 5 = 0.
$$[/tex]

Multiplying by [tex]$-1$[/tex] for a positive leading coefficient results in

[tex]$$
7x^4 - 3x^3 + 7x^2 + 2x - 5 = 0.
$$[/tex]

This is an equivalent form, but the equation that was directly set up from the system is

[tex]$$
3x^3 - 7x^2 + 5 = 7x^4 + 2x.
$$[/tex]

Thus, the answer is option 2.