XZ = " 5.831 units " .
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XY = 3 units (obtained from counting on the graph provided).
YZ = 5 units (obtained from counting on graph provided). 
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To find ZX (the hypotenuse); use the Pythogorean Theorem:
 → 3² + 5² = c² ; in which "c" = ZX ; 
 → c² = 3² + 5² = 9 + 25 = 34 ;
 → c² = 34 ; 
To find "c" ; take the positive square root of each side of the equation; 
 to isolate "c" on one side of the equation; & to solve for "c" ; 
 → √(c²) = √34 ; 
 → c = 5.8309518948453005 ; 
 → round to: "5.831 "
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