"negative number" - A number that is defined to produce -a + a = 0
"imaginary numer" - A number "i" which is the square root of negative one
"Integer" - A whole number that is not expressed as a fraction.
"Complex number" - A number with both a real and imaginary part.

Imaginary Number is a number with square that is negative like i^2 = -1
Complex Number is a number consisting of a real part and an imaginary part like a + bi (where i^2= -1).
Pythagoras Theorem is a theorem that tells about sides of a right angle triangle.