Expert: Sherry Wallin - 11/2/2010

Question
QUESTION: What would the graph look like for (3+2i)-(-7+5i)?
Also for (3+i)(-3-4i)?

ANSWER: Elizabeth~

Simplify first: 3+7 + 2i -5i = 10 - 3i, which means 10 units to the right on the "real" axis (x axis) and 3 units down on the imaginary axis, y-axis.

Math Prof

---------- FOLLOW-UP ----------

QUESTION: What would the geometric representation on the graph look like?
What would the geometric representation for (3+i)(-3-4i) look like?

Answer
Elizabeth~

For the problem I answered above the geometric representation is the point (10,-3).

For the second one you need to multiply and simplify:
(3+i)(-3-4i)
= 3(-3-4i) + i(-3-4i)
= 3(-3) + 3(-4i) + i(-3) + i(-4i)
= -9 + -12i + -3i + -4i^2
= -9 + -15i + -4(-1)
= -9 + -15i + 4
= -9 + 4 + -15i
= -5 + -15i

and geometrically this is the point (-5, -15) on the graph.

Math Prof