# arch tanget

#### shermaine

##### New Member
hi,

may i know how to get arch tanget for -1.16?
When in calculator, radian mode, i use tan inver -1.16, but i cant get 2.28

#### Roff

##### Well-Known Member
hi,

may i know how to get arch tanget for -1.16?
When in calculator, radian mode, i use tan inver -1.16, but i cant get 2.28
The tangent function repeats every π radians. For x=arctan(y), Your calculator will give you the principal value, which is located in the interval -π/2 ≤ y ≤ π/2. 2.28 is greater than π/2. Take arctan(-1.16) and add π to the result, and you will get 2.28.

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#### shermaine

##### New Member
yes, thanks! i got another one, inverse cos of -2/sq root 20, how do i get 242 degree?

#### Miles Prower

##### Member
yes, thanks! i got another one, inverse cos of -2/sq root 20, how do i get 242 degree?
You can't.

arccos(-2 / sqrt(20)= 116.565deg

360 - 116.565= 243.435deg