Question

Select the choice below that could be the first step in solving the following system of equations using elimination:
-7x + 5y = -12
8y − 3x + 3 = 0

A. Write the second equation in terms of x.
B. Replace the right side of the first equation with the second equation.
C. Multiply the second equation by -7.
D. Multiply the first equation by -5.

Answer 1

A

Answer 2

@tvcong : whys that ?

Answer 3

You should try it to see if it is the first step.

Answer 4

i dont understand what writing the second equation in te

Answer 5

*terms of x means

Answer 6

I think it means solving for y, and y is expressed in terms of x.

Answer 7

I would multiply the second equation by -7 as the first step. From there you could multiply the first equation by three and subtract them to eliminate x from one giving you y which you can use to get x.

Answer 8

A. Write the second equation in terms of x.
it mean write rewrite equtionn like this


-7x + 5y = -12
8y − 3x +=-3

Answer 9

put into an augmented matrix

\[\left[\begin{matrix}-7 & 5 & -12 \\ -3 & 8 & -3\end{matrix}\right]\]
multiply second row by -7
\[\left[\begin{matrix}-7 & 5 & -12 \\ 21 & -56 & 21\end{matrix}\right]\]
multiply first row by -3
\[\left[\begin{matrix}21 & -15 & 36 \\ 21 & -56 & 21\end{matrix}\right]\]
subtract second from first
\[\left[\begin{matrix}21 & -15 & 36 \\ 0 & 41 & 15\end{matrix}\right]\]

so 41y=15 ==> y=15/41

and 21x-15y=36
21x-15*15/41=36
21x=1704/41 ==> x=81/41

so the solutions are x=81/41 and y=15/41.

As you can see, the first step I took was multiplying the second equation by negative 7, and I was able to solve the equation without ever dividing it by 7 (you can start with ANY of these and then "undo" them later and arrive at the solution), therefore the answer "C" is satisfied

Answer 10

the method I used is called the "method of elimination" so C is definitely the answer