Determine whether each set of measures can be sides of right triangle. then determine whether they form a pythagorean triple.
4. 11, 18, 21
5. 21, 72, 75
6. 7, 8, 11
7. 9, 10, √161
8. 9, 2 √10 , 11
9. √7 , 2 √2 , √15

⇒ Pythagorean triple
 
Pythagorean triple are set of positive integers. All sums are positive. The  is the longest side of a triangle. 
 
+  = 

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⇒ 11, 18, 21 
This can`t be a right triangle. They do not form a Pythagorean Triple.

⇒ 21, 72, 75 
This can be a right triangle. It forms a Pythagorean Triple.  

⇒ 7, 8, 11 
This can not be a right triangle. It does not form a Pythagorean Triple.

⇒ 9, 10, √161 
This can not be a right triangle, It is not a Pythagorean Triple.

⇒  9, 2 √10 , 11  
This can not be a right triangle. It is not a Pythagorean Triple 

 ⇒ √7 , 2 √2 , √15 
This can not be a right triangle. It is not a Pythagorean Triple .

The answer should be c.