Find $( 3 + 9 i ) ( - 4 - 5 i )$ and express the answer in the standard form of a complex number.
A) $- 57 - 36 i$
B) $33 + 51 i$
C) $- 12 - 45 i$
D) $33 - 51 i$

Question

Quizplus · Accepted Answer

To multiply two complex numbers, use the distributive property: $(3 + 9i)(-4 - 5i) = 3(-4) + 3(-5i) + 9i(-4) + 9i(-5i)$. This simplifies to $-12 - 15i - 36i - 45i^2$. Since $i^2 = -1$, $-45i^2 = 45$. Combine like terms: $-12 + 45 - 51i = 33 - 51i$.

Find (3+9i)(−4−5i)( 3 + 9 i ) ( - 4 - 5 i )(3+9i)(−4−5i)

Find $( 3 + 9 i ) ( - 4 - 5 i )$