Question

Solve using elimination method (4x-5y = 21(2x+5y = 0

Answer 1

`\begin{gathered} Given \\ 4x-5y=21\text{ and 2x+5y=0} \end{gathered}`
`\begin{gathered} Let \\ 4x-5y=21-----(1) \\ 2x+5y=0------(2) \end{gathered}`
`Equation\text{ \lparen1\rparen plus equation \lparen2\rparen}`

`\begin{gathered} 6x+0=21 \\ 6x=21 \\ x=(21)/(6) \\ x=(7)/(2) \end{gathered}`
`plug\text{ x=}(7)/(2)\text{ into equation \lparen2\rparen to obtain y;}`
`\begin{gathered} 2x+5y=0 \\ ie\text{ 2\lparen}(7)/(2)\text{\rparen+5y=0} \\ 7+5y=0 \\ 5y=-7 \\ y=-(7)/(5) \end{gathered}`

Final answer:

`\begin{gathered} x=(7)/(2) \\ y=-(7)/(5) \end{gathered}`