In a triangle PQR. Q=8cm , R=6cm . Cosp=1/12.calculatethe value of p

Answer 1

I think you mean:
In a triangle PQR. q=8cm , r=6cm . Cos(P)=1/12. Calculate the value of p.

where capital letters mean vertices, lower-case letters mean lengths of sides opposite the corresponding vertex.

Use cosine rule:
p²=q²+r²-2qr(cos(P))
and solve for p.