Which of the following quadratic equations has equal roots?

A quadratic equation : $$ax^2 + bx + c = 0$$ has equal roots iff Discriminant, $$D = b^2 - 4ac = 0$$

(A) : $$x^2 + 14x - 49 = 0$$

=> D = $$(14)^2 - 4(1)(-49) = 196 + 196 = 392 \neq 0$$

(B) : $$x^2 + 7x + 49 = 0$$

=> D = $$(7)^2 - 4(1)(49) = 49 - 196 = -147 \neq 0$$

(C) : $$x^2 - 7x - 49 = 0$$

=> D = $$(-7)^2 - 4(1)(-49) = 49 + 196 = 245 \neq 0$$

(D) : $$x^2 + 14x + 49 = 0$$

=> D = $$(14)^2 - 4(1)(49) = 196 - 196 = 0$$

Thus, the equation : $$x^2 + 14x + 49 = 0$$ has equal roots.