Answer:
c
Step-by-step explanation:
given x = 5 + i[tex]\sqrt{7}[/tex] then y = 5 - i[tex]\sqrt{7}[/tex]
x² - 2xy + y² ← is a perfect square
= (x - y)² ← substitute values for x and y
= (5 + i[tex]\sqrt{7}[/tex] - (5 - i[tex]\sqrt{7}[/tex] )²
= (5 + i[tex]\sqrt{7}[/tex] - 5 + i[tex]\sqrt{7}[/tex] )²
= (2i[tex]\sqrt{7}[/tex] )²
= 2² × i² × ([tex]\sqrt{7}[/tex] )²
= 4 × - 1 × 7
= - 28
