Solution :
Given a right triangle with hypotenuse 85 and legs 84 and y.
Use Pythagoras theorem, to find the length of the leg y of the right triangle.
According to Pythagoras theorem,
![(hypotenuse)^(2) = leg_(1)^(2)+leg_(2)^(2)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/2k4h8fi81zdkj7e89p0pa9w2g0zwiznk33.png)
As given in the question,
![hypotenuse = 85 \\\\leg_(1) = 84\\\\leg_(2) = y](https://img.qammunity.org/2019/formulas/mathematics/middle-school/23zszgbco7e1z4yoyx1soaqlai5pzvyrrv.png)
Put these values,
![\Rightarrow 85^(2)=84^(2) +y^(2) \\\\\Rightarrow y^(2)=85^(2)-84^(2)\\\\\Rightarrow y =\sqrt{85^(2)-84^(2)} \\\\\Rightarrow y =√(169)\\\\\Rightarrow y =13](https://img.qammunity.org/2019/formulas/mathematics/middle-school/v94v88r4qzov62ecgsao4d9trjph7qwcdx.png)
Hence, the length of leg y =13.