Posted by Courtney on Wednesday, February 20, 2008 at 5:50pm.
find the modulus and the argument of the following complex numbers:
15-4i and a-ai where a is greater than 0
calculus - Damon, Wednesday, February 20, 2008 at 6:10pm
if z = a + b i
r^2 = sqrt( a^2 + b^2)
and a = r cos T
and b = r sin T
if a = 15
and b = -4
then r^2 = 15^2 + (-4)^2 = 225+16
r = 15.524
cos T = 15/15.524
so T = 14.9 or -14.9
sin T = -4/15.52
so T = -14.9 or (180-14.9)=165.1
T = -14.9 which is +345.1 in the fourth quadrant satisfies both, so that is it. (Besides we could see that 15-4i was in quadrant 4)
r = sqrt (2 a^2) = a sqrt 2
fourth quadrant again
sin T = -1/sqrt (2) = = -.707
T = -45 degrees which is + 315 degrees
calculus - Damon, Wednesday, February 20, 2008 at 6:34pm
I did them as two different questions
modulus = r = 15.524
argument = T (for theta) = -14.9 degrees (or +345.1 degrees)
modulus = a sqrt 2
theta = argument = -45 (or 315) degrees
calculus - Courtney, Wednesday, February 20, 2008 at 6:37pm
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