Final answer:
To justify the statement 'If ZA and ZB are complementary, then mZA + mZB = 90,' we reference the definition of complementary angles, which are two angles whose measures add up to 90 degrees, as well as the commutative property of addition.
Step-by-step explanation:
The question asks to justify the mathematical statement that if angles ZA and ZB are complementary, then the sum of the measures of angles ZA and ZB is 90 degrees (mA + mB = 90). In mathematics, complementary angles are defined as two angles whose measures add up to 90 degrees. Therefore, if ZA and ZB are complementary by definition, it justifies the equation mZA + mZB = 90.
This concept also relates to the commutative property of addition, which tells us that the order in which two numbers are added does not affect the sum; that is, A + B = B + A. This means that whether you add the measure of angle ZA to angle ZB or vice versa, the result is the same and should equal 90 degrees for complementary angles.