triangle, if I know side-side-side

I can draw the triangle with this JavaScript file:

//  base = 160 (16 quadretti/squares)
//  scegli/choose K (distance of base from left edge) = 0 or 10 or 20 or ... 
//  scegli/choose M: numero per cui moltiplicare a,b,c in modo che rimangano nel box
//                   number by which to multiply a,b,c so that they remain in the box
K = 10
a = 1; b = Math.sqrt(2); c = 1
M = 100
grid="grey"        // grid="grey"   -> grid="white" per nessuna griglia  / no grid
angle="green"      // angle="green" -> angle="white" per nessuna scritta sugli angoli / no note
side="blue"        // side=="blue"  -> side="white"  per nessuna scritta sui lati / no note
            OR
K = 20
a = 1; b = 1; c = Math.sqrt(2)
M = 80

What is the amplitude of the angles of the triangle PQR with P = (2, -1, -1), Q = (0, 1, -2), R = (1, -3, 1)?

With this script I find QR, QP and PR:

 

Then QP = PR, and ∠RQP, ∠PRQ, ∠QPR, are: