**[ 1 2 -1 ]**

**[ 2 5 -(a+2) ]**

**[ -1 a-5 1 ]**

so i typed:

**[ 1 2 -1 ]**

**det(**

**[ 2 5 -(a+2) ]**

**)**

**[ -1 a-5 1 ]**

but i got an error message: "Incorrect Argument"

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Secondly, I wish to know how to solve these three simultaneous equations for "a" on the classpad

**x + 2y -z = 2**

**2x + 5y -(a+2)z = 3**

**-x + (a+5)y + z = 1**

I tried using the solve function on the 2D menu, but i got the error message: "Invalid Dimension"

Thanks in advance for any help.