Solve the Equation After Making an Appropriate Substitution $$x ^ { 4 } - 50 x ^ { 2 } + 49 = 0$$

Multiple Choice

Solve the equation after making an appropriate substitution.
- $$x ^ { 4 } - 50 x ^ { 2 } + 49 = 0$$

A) $\{ - 49,49 \}$
B) $\{ - 50,50 \}$
C) $\{ - 1,1 , - 7,7 \}$
D) $\{ - 7,7 \}$