The standard form for a complex number is: $a+ib$ or $x+iy$ where: "a" and "x" are the real parts of the complex number, and; "b" and "y" being the imaginary part of the complex number. when you want to find the trigonometric form you're looking for the mod-arg form: $Rcis\theta=R(\cos\theta + i\sin\theta)$ Where R is the modulus of the complex number; "cos(theta)" being the real part; "sin(theta)" being the imaginary part, and; "theta" being the argument of the complex number. For your example being -4. We should find the the modulus first using the Phythagorean formula: $R=\sqrt{a^2+b^2}$ $=\sqrt{(-4)^2+0^2}$ $=\sqrt{16}$ $=4$ Now you should find the angle or argument of -4. Use this graph to find the angle you're looking for: |dw:1371802552197:dw| Then you can connect all the information you gathered- the modulus (the distance) and the argument (the angle); so now you can put all that into the mod-arg form given to you by me.