Question: Résolution of a*cos(gamma)+b*sin(gamma)+c=0

Hello,

I would like to solve easily this equation with maple.

When i use solve or isolate functions, i have a result with arctan function.

"sol := solve(a*cos(gamma)+b*sin(gamma)+c, gamma):
isolate(a*cos(gamma)+b*sin(gamma)+c=0,gamma); "

It is good but i would like solutions with arccos.

In other words, i would like to have these calculations :

a*cos(gamma)+b*sin(gamma)+c=0

cos(psi)=a/sqrt(a²+b²)

sin(psi)=b/sqrt(a²+b²)

thus 

cos(psi)*cos(gamma)+sin(psi)*sin(gamma)=-c/sqrt(a²+b²)

cos(psi+gamma)=-c/sqrt(a²+b²)

gamma=-psi -/+ arccos(c/sqrt(a²+b²))

Is there a possibility to lead this calculation automatically with maple? For example, is it possible to force isolate function to seek for this kind of solution.

Thanks a lot for your help