Completely factor the following expression.

`z^2 + 15z - 54`

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To factorize `z^2 +15z-54` you need to establish the factors that are relevant between the first and the third terms:

`z^2 = z times z` and the factors of 54 are (1 x 54, 2 x 27, 3 x 18,

6 x 9, ) . Use must establish which of these combinations will render a middle term of +15

The only ones that will work are 3x18. Care must be taken not to use 6 x9 which seem s most obvious but would render +54 as the third term .

`therefore= (z-3)(z+18)`

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