Answer :

bookgirl9632
For any triangle problem with finding a length, use the Pythagorean theorem; [tex] a^{2} + b^{2} = c^{2} [/tex]
x=17cm, y=8cm
17²+8²=z²
289+64=z²
353=z²
√353=√(z²)
√353=z
The answer is D: √353 cm
Pathagreom therom a^2+b^2=c^2 where c is the hypotenuse, or the longest side

so you have (8)^2 + z^2 = (17)^2

so 64 + z^2 = 289

next subtract 64 from the left and right side of the equation
64 + z^2 = 289
-64            -64

z^2=225
 then take the square root and you get z=15