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## keep just positive or just negetive answer of acos?

Najmeh Eskandari

### Najmeh Eskandari (view profile)

さんによって質問されました 2018 年 8 月 12 日

### jonas (view profile)

さんによって 編集されました 2018 年 8 月 13 日
jonas

### jonas (view profile)

さんの 回答が採用されました
I have arccos and I want to keep just negative answer of it? how can I do it?(there are two answer)

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### jonas (view profile)

2018 年 8 月 12 日
採用された回答

If A is a vector with your answers. Remove non-negatives by
A(A>=0)=[]

Najmeh Eskandari

### Najmeh Eskandari (view profile)

2018 年 8 月 13 日
no it is inverse cos and has two answers. i want to keep positive answer and think it is not a vector.
jonas

### jonas (view profile)

2018 年 8 月 13 日
I don't understand. What function did you use? The fact that you want to keep only one value implies that you have two, hence my simple fix.
MATLAB's acos however only returns a single positive solution. If you want a negative solution, just multiply by -1, as cos(x)=cos(-x)
"For real elements of x in the interval [-1,1], acos(x) returns real values in the interval [0,pi]." - the doc

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