To find the length of a segment you can use the pythagorean theorem: given two points
you have
![\overline{AB} = √((x_A-x_B)^2+(y_A-y_B)^2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/m4gikk6m0pcoq8saq4xw6flg6n7tc708ap.png)
In your case, we have
![\overline{RS} = √((x_R-x_S)^2+(y_R-y_S)^2) = √((0-b)^2+(a-c)^2) = √(b^2+(a-c)^2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/cy76bkhe7lm2jejwcz51ulaga0y2j55p6s.png)
Note that your exercise seems to suggest the opposite, i.e.
![\overline{RS} = √(b^2+(c-a)^2)](https://img.qammunity.org/2020/formulas/mathematics/high-school/9gpa6vc74j3xb73vx43wa8k7e4e76e01lk.png)
Don't worry: the two numbers are the same. In fact,
and
are opposite, and opposite numbers are the same when squared (for example,
)
It had to be so after all: we're simply claiming that the distance between R and S or between S and R is the same..how could it be any different?