Question

Solve the system by substitution. y = -4x 23 - 5y = 44

Answer 1

Explanation

• Given the system of equations.

$\begin{cases} y = - 4x \\ 23 - 5y = 44 \end{cases}$

• Substitute y = -4x in the second equation.

$23 - 5( - 4x) = 44 \\ 23 + 20x = 44 \\ 20x = 44 - 23 \\ 20x = 21 \\ x = \frac{21}{20}$

• Substitute the value of x in any given equations. I will substitute the value of x in the first equation.

$y = - 4x \Longrightarrow y = - 4( \frac{21}{20} ) \\ y = \cancel{ - 4}( \frac{21}{ \cancel{20}} ) \Longrightarrow y = - \frac{21}{5} \\ y = - \frac{21}{5}$

• Answer Check by substituting both values in two equations.

First Equation

$y = - 4x \Longrightarrow - \frac{21}{5} = - 4( \frac{21}{20} ) \\ - \frac{21}{5} = \cancel{ - 4}( \frac{21}{ \cancel{20}} ) \\ - \frac{21}{5} = - \frac{21}{5} \: \: \: \checkmark$

Second Equation

$23 - 5y = 44 \\ 23 - 5( - \frac{21}{5} ) = 44 \\23 - \cancel{5}( - \frac{21}{ \cancel{5}} ) = 44 \\ 23 + 21 = 44 \\ 44 = 44 \: \: \: \: \checkmark$

Both equations are true for the value of x and value of y.

Answer

$\begin{cases} x = \frac{21}{20} \\ y = - \frac{21}{5} \end{cases}$

Coordinate Point form

$( \frac{21}{20} , - \frac{21}{5} )$