Given planes P1:x+2y+3z−4=0 P2:2x+y−z+5=0 The equation pf plane through intersection of P1 and P2 is P1λP2=0 ⇒ (x+2y+3z−4)+λ(2x+y−z+5)=0 ⇒ x(1+2λ)+y(2+λ)+z(3−λ)+(5λ−4)=0 ....(i) Since, the plane is perpendicular to 5x+3y+6z+8=0 ∴ a1a2+b1b2+c1c2=0 ⇒ (1+2λ)(5)+(2+λ)(3)+(3−λ)(6)=0 ⇒ 5+10λ+6+3λ+18−6λ=0 ⇒ 7λ+29=0 ∴ λ=