Answer: (x+7i)(x-7i)
Step-by-step explanation: if we distribute the terms on the first choice, we get x^2 +7ix - 7i x -49i^2. The two terms in the middle cancel each other out, leaving us with only x^2 - 49i^2. i^2 = -1. so we have x^2- 49(-1)=x^2-(-49)= x^2 +49
