We have the following:
We must pass each equation to the following form:
![y=mx+b](https://img.qammunity.org/2023/formulas/mathematics/high-school/smsb8cbft03lwblmi49nf2l6jby2ofxzws.png)
where m is the slope
when two lines are parallel the slopes are equal, when they are perpendicular they are inverse
therefore,
![\begin{gathered} -4x+5y=20 \\ 5y=4x+20 \\ y=(4)/(5)x+4 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/2ltxrp8ufgo12phe4l1f383jfsk9fpo6ww.png)
The slope is 4/5, the inverse is -5/4
now, for:
![\begin{gathered} -x+5y=15 \\ 5y=x+15 \\ y=(1)/(5)x+3 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/1uw8mi5fug2pm4oo70u4hkxh963qpifizr.png)
therefore, they are neither parallel nor perpendicular
![\begin{gathered} 7x+3y=-18 \\ 3y=-7x+18 \\ y=-(7)/(3)x+6 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/abjqb21j4tf2dfutl0lnxzlxby36uornca.png)
therefore, they are neither parallel nor perpendicular
![\begin{gathered} -3x+7y=14 \\ 7y=3x+14 \\ y=(3)/(7)x+2 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/12qzg8p3cpptxvflk60gi99w57gmkrc5x6.png)
therefore, they are neither parallel nor perpendicular
![\begin{gathered} 7x-3y=5 \\ 3y=7x-5 \\ y=(7)/(3)x-(5)/(3) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ph3axw6bfweqcngmcndk0alcwmmslkxxc8.png)
therefore, they are neither parallel nor perpendicular
7x + 3y =-18 and - 3x + 7y = 14 are perpendicular