We need to find θ in radians (see Trigonometric Functions of Any Angle if you need a reminder about reference angles) and *r*.

`alpha=tan^(-1)(y/x)` `=tan^(-1)(5/1)` `~~1.37text( radians)`

[This is `78.7^@` if we were working in degrees.]

Because our angle is in the second quadrant, we need to apply:

`theta = pi - 1.37 ~~1.77`

And

`r=sqrt(x^2+y^2)`

`=sqrt( (-1)^2 + (5)^2 )`

`= sqrt(26)`

` ~~ 5.10`

So `-1 + 5j` in **exponential** form is
`5.10e^(1.77j)`

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