# Math Help - modulus and argument

1. ## modulus and argument

find the modulus and argument of

(a)6+j
(b)-5-9j

do i sub into
$\sqrt{a^2+b^2}$

and
$tan^{-1}\frac{a}{b}$

many thanks

2. Originally Posted by decoy808
find the modulus and argument of

(a)6+j
(b)-5-9j

do i sub into
$\sqrt{a^2+b^2}$

and
$tan^{-1}\frac{a}{b}$

many thanks
For $z = a + jb$ where $j^2 = -1$

You have your trig ratio wrong, the imaginary axis implies the opposite and the real axis the adjacent

therefore $\arg (z) =\arctan \left(\frac{b}{a}\right)$

Otherwise good