a^→ =i^ +3j^ +4k^ b^→ =2i^ −3j^ +4k^ c^→ =5i^ −2j^ +4k^ given that p^→ ×b^→ =b^→ ×c^→ and p^→ .b^→ =0 then the value of p^→ (i^ −j^ +k^ )is