If a→,b→,c→ are three non-coplanar and p→,q→,r→ are reciprocal vectors to a→,b→ and c→ respectively, then la→+mb→+nc→⋅lp→+mq→+nr→ is equal to : (where 1,m,n_ are scalars)

p→   =  b→ × c→a→   b→   c→  ;  q→  =  c→ × a→a→   b→   c→ ;  r→  = a→ × b→a→   b→   c→a→.p→=a→·  b→ × c→a→   b→   c→=a→   b→   c→a→   b→   c→=1    and a→.q→=a→·  c→ × a→a→   b→   c→=a→   c→   a→a→   b→   c→=0similarly b→·q→ =1  c→·r→=1 la→+mb→+nc→⋅lp→+mq→+nr→ =l2a→·p→ +m2b→.q→+n2c→·r→  =l2+m2+n2