You need to evaluate the absolute value of the given complex number, using the following formula, such that:

`|z| = sqrt(x^2 + y^2)`

Identifying the real part x and the imaginary part y, yields:

`{(x = 1),(y = -2):}`

Reasoning by analogy, yields:

`|z| = sqrt(1^2 + (-2)^2)`

`|z| = sqrt(1 + 4)`

`|z| = sqrt 5`

**Hence, evaluating the absolute value of the given complex number, yields **`|z| = sqrt 5.`

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