Which of the following is/are correct? (a)If ` vec a= hat i+ hat j` and ` vec b=2 hat i- hat k` then the point of intersection of the lines ` vec r `x`vec a`= `vec b` x `vec a` and ` vec a`x `vec b`=` vec a`x` vec b` is 3` vec i`+` vec j`-`veck` (b)(` vec r``dot` `hat i`)( `hat i` x `vec r`)+( `vec r `dot `hat j`)( `hat j `x `vec r`)+(` vec r `dot `hat k`)(` hat k` x` vec r`)= `vec0` (c)If `| vec a|=3,| vec b|=5,| vec c|=7` and ` vec a+ vec b+ vec c= vec0` then the angle between ` vec aa n d vec b` is `pi/3` (d)If the vectors ` vec a , vec b& vec c` from the sides `B C ,C A&A B` respectively of a triangle `A B C` , then ` vec a`x` vec b`= `vec b`x` vec c`x `vec a`