How do you multiply (1+3i)(1-3i) (1+3i)(1−3i) in trigonometric form?
1 Answer
Mar 27, 2016
(1 + 3i)(1 - 3i) = 10(1+3i)(1−3i)=10
Explanation:
abs(1+3i) = abs(1-3i) = sqrt(1^2+3^2) = sqrt(10)|1+3i|=|1−3i|=√12+32=√10
1 + 3i = sqrt(10) cis (arctan(3))1+3i=√10cis(arctan(3))
1 - 3i = sqrt(10) cis (arctan(-3)) = sqrt(10) cis (-arctan(3))1−3i=√10cis(arctan(−3))=√10cis(−arctan(3))
So:
(1 + 3i)(1 - 3i)(1+3i)(1−3i)
= (sqrt(10) cis (arctan(3)))(sqrt(10) cis (-arctan(3)))=(√10cis(arctan(3)))(√10cis(−arctan(3)))
= (sqrt(10))^2 cis (arctan(3) - arctan(3))=(√10)2cis(arctan(3)−arctan(3))
= 10 cis(0)=10cis(0)
= 10=10