Texas Instruments TI-83 PLUS - Manual (Page 93)

TI-83 Plus Math, Angle, and Test Operations 90
angle(
angle( returns the polar angle of a complex number or list of complex
numbers, calculated as tan L 1 (b/a), where b is the imaginary part and a is
the real part. The calculation is adjusted by + p in the second quadrant or
Np in the third quadrant.
angle( a + bi ) returns tan L 1 (b/a) .
angle( r e^( qi )) returns q , where Lp < q < p .
abs(
abs( (absolute value) returns the magnitude (modulus), (real2+imag2) , of
a complex number or list of complex numbers.
abs( a + bi ) returns (a2+b2) .
abs( r e^( qi )) returns r (magnitude).