For this case we have by definition, if two lines are perpendicular then the product of their slopes is -1.
![m_ {1} * m_ {2} = - 1](https://img.qammunity.org/2020/formulas/mathematics/high-school/bmbuwrtpmwf6qqw1n50skztkvkgpuhgvuw.png)
We have the following equation:
![28x-7y = 9](https://img.qammunity.org/2020/formulas/mathematics/middle-school/raxce10f42jooquh9e98yr1stobzff15qi.png)
Rewriting we have:
![28x-9 = 7y\\y = \frac {28x-9} {7}\\y = 4x- \frac {9} {7}](https://img.qammunity.org/2020/formulas/mathematics/middle-school/fnh460qoscixvjvf97ipvxud1beqkiqtoo.png)
The slope of this line is 4.
We found
![m_ {2}:](https://img.qammunity.org/2020/formulas/mathematics/middle-school/7w2u7y045j3jv6u4cqqkzdj6m829lmgort.png)
![m_ {2} = \frac {-1} {m_ {1}}\\m_ {2} = \frac {-1} {4} = - \frac {1} {4}](https://img.qammunity.org/2020/formulas/mathematics/middle-school/2gqceftmeu84kjacs8h5o2uo7n32c34v20.png)
The new line is of the form:
![y = - \frac {1} {4} x + b](https://img.qammunity.org/2020/formulas/mathematics/middle-school/zmzh681cvjn0uhw8y0l8vwwju2sdtj0a6u.png)
We substitute the given point to find the cut point "b":
![1 = - \frac {1} {4} (4) + b\\1 = -1 + b\\b = 2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/11ub17ui859pdskpthvp72m93baunhrc1f.png)
Finally, the equation is:
![y = - \frac {1} {4} x + 2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/t3o1yu55fz84um5c3yzpy50ph0povmmtai.png)
Answer:
![y = - \frac {1} {4} x + 2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/t3o1yu55fz84um5c3yzpy50ph0povmmtai.png)