Answer:
Step-by-step explanation:
Pythagorean theorem works for right triangles  a²+b² = c²
The Pythagorean theorem might be easier to understand written like this ......
(side 1)² + (side 2)² = (hypotenuse)²           hypotenuse is c in this diagram    
it can also be written like this just flipping both sides (they are still equal)
 (hypotenuse)² = (side 1)² + (side 2)² 
using algebra to solve for the hypotenuse
 hypotenuse  =  √[ (side 1)² + (side 2)²]         remeber    hypotenuse = c
 c  =  √[ (side 1)² + (side 2)²]                     rewritten with c instead of hypotenuse
     = √[      4²      +     3²   ]
     = √(      16      +     9    ]
     = √(25)
What number is the square root of 25?   
Or what number times itself equals 25?
 
Your chooses were ......  A B C or D
 A  5x5 = ?
 B  7x7 =  ?
 C  16x16 = ?
 D   15x15 = ?