Given that P + Q = R and that R is perpendicular to P. If IPI = IRl, then what is the angle between P and a ?

Given P+Q=R or R-P=QSince R is perpendicular to P, therefore,R2 + P2 = Q2But P=R. Hence R=Q/2=PSo, cos⁡θ=R2−P2−Q22PQ=Q22−Q22−Q22Q2(Q)=−Q22Q2=−12θ=135∘ or 3π/4rad