High School

Which system is equivalent to

\[
\begin{cases}
5x^2 + 6y^2 = 50 \\
7x^2 + 2y^2 = 10
\end{cases}
\]

?

A.

\[
\begin{cases}
5x^2 + 6y^2 = 50 \\
-21x^2 - 6y^2 = 10
\end{cases}
\]

B.

\[
\begin{cases}
5x^2 + 6y^2 = 50 \\
-21x^2 - 6y^2 = 30
\end{cases}
\]

C.

\[
\begin{cases}
35x^2 + 42y^2 = 250 \\
-35x^2 - 10y^2 = -50
\end{cases}
\]

D.

\[
\begin{cases}
35x^2 + 42y^2 = 350 \\
-35x^2 - 10y^2 = -50
\end{cases}
\]

Answer :

To solve this problem, we need to find an equivalent system of equations to the given one:

Original system:
1. [tex]\(5x^2 + 6y^2 = 50\)[/tex]
2. [tex]\(7x^2 + 2y^2 = 10\)[/tex]

To find an equivalent system, we can scale and manipulate these equations. We'll proceed as follows:

1. Scale the equations to eliminate a variable:
- Multiply the first equation by 7:
[tex]\[
7(5x^2 + 6y^2) = 7 \times 50
\][/tex]
This gives:
[tex]\[
35x^2 + 42y^2 = 350
\][/tex]

- Multiply the second equation by 5:
[tex]\[
5(7x^2 + 2y^2) = 5 \times 10
\][/tex]
This gives:
[tex]\[
35x^2 + 10y^2 = 50
\][/tex]

2. Subtract the second scaled equation from the first scaled equation:

- Subtraction:
[tex]\[
(35x^2 + 42y^2) - (35x^2 + 10y^2) = 350 - 50
\][/tex]
Simplify the left side:
[tex]\[
42y^2 - 10y^2 = 32y^2
\][/tex]
The right side:
[tex]\[
350 - 50 = 300
\][/tex]
So the equation simplifies to:
[tex]\[
32y^2 = 300
\][/tex]

3. Check and simplify the system:
- We derived the system:
[tex]\[
35x^2 + 42y^2 = 350
\][/tex]
[tex]\[
-35x^2 - 10y^2 = -50
\][/tex]

After these steps, the equations form the equivalent system:

1. [tex]\(35x^2 + 42y^2 = 350\)[/tex]
2. [tex]\(-35x^2 - 10y^2 = -50\)[/tex]

Thus, the equivalent system corresponds to the fourth option:

[tex]\[
\left\{\begin{aligned}
35x^2+42y^2 & = 350 \\
-35x^2-10y^2 & = -50
\end{aligned}\right.
\][/tex]