Which of the following equations represents the pythagorean theorem?
c = a + b
ab = ba

The theorem is a²+b²=c²
Rewritten it is √(a²+b²) = c

The correct answer is:  " c = √(a² + b²) " .

Explanation:

The Pythagorean theorem is:  a² + b² = c² .

↔   c² = a² + b² ;

Take the square root of EACH SIDE OF THE EQUATION;

→  √(c²) = √(a² + b²) ;

→  c =  √(a² + b²) ; which is one of the two answer choices given; which is correct.

Note:  The other answer choice given:

m = (y₂ − y₁) / (x₂ − x₁) ;  refers to the calculation of the slope of a line; given an equation for a line, in "slope-intercept form"; that is, "y = mx +b" ;  in which "m" is the slope, given the coordinate of two points on the line: 

            →   (x₁, y₁) ;  and:   (x₂, y₂)  ;


which is NOT related to the "Pythagorean theorem" equation.