What is the missing justification in the proof?
a) symmetric property of equality
b) substitution property of equality
c) reflexive property of equality
d) transitive property of equality

The missing justification in the proof is
B) Substitution property of equality

The expression for sin² x and cos² x is substituted to the other side of the equation. Since sin x = a/c, then sin² x = a²/c². Similarly, since cos x = b/c, then cos² x = b²/c². Adding to two results to the third statement.

6xy and -16xy000000000