121x² + 36y²
= 121x² - (-36y²) Notice that the first and last term are perfect squares.
= (11x - 6iy)(11x + 6iy) So, you can factor using the difference of squares.
Answer: B
(11x + 6iy)(11x - 6iy)
using the difference of squares identity
a² - b² = (a - b)(a +b)
a² + b² = (a - bi )(a + bi)
121x² = ( 11x)² ⇒ a = 11x and 36y² = (6y)² ⇒ b = 6y
121x² + 36y² = (11x - 6iy)(11x + 6iy)
