let a=i+4j+2k,b=3i-2j+7k and c=2i-j+4k. Find a vector which is perpendicular to both a and b,and c.d=15

Question

phi · Answer

do you know how to find the cross product of a and b ?

kanwal32 · Answer

yes

kanwal32 · Answer

@phi

kanwal32 · Answer

@phi yes i know

phi · Answer

what did you get?  a x b will give you a vector perpendicular to both vector a and vector b

kanwal32 · Answer

@ganeshie8

kanwal32 · Answer

@mathmale @ShadowLegendX

kanwal32 · Answer

@ganeshie8

kanwal32 · Answer

@Jaynator495

jaynator495 · Answer

@ganeshie8 @Directrix OH I KNOW @mathmale 

@mathmale ya think you can help in math? XD

thephysicsman · Answer

don't remember this could be dot product or cross product.

kanwal32 · Answer

@hartnn hlp

mathmale · Answer

If you want to find a vector perpendicular to both vector a and vector b, yes, you must find the cross product of vector a with vector b.

mathmale · Answer

I could give you better feedback if you'd show all of your work.

kanwal32 · Answer

ok

mathmale · Answer

the vector cross product is good only in three dimensions (which you have here).

Be sure you have the proper formula for the cross product before you begin.

thephysicsman · Answer

are you taking calc-III ? @kanwal32

kanwal32 · Answer

so i assumed vector d as xi+yj+zk
then i did dot product with a and b and make it zero

kanwal32 · Answer

someone help

kanwal32 · Answer

@mathmale

kanwal32 · Answer

then i did c.d=15

hartnn · Answer

since you know how to do "cross" product (and not dot),
please tell us what you get for 
$\Large \bar a \times \bar b$

kanwal32 · Answer

32i+j-14k

mathmale · Answer

Yes, echoing both phi and hartnn, you MUST find the CROSS product of vector a with vector b to obtain a new vector which will be perpendicular to vectors a and b.

mathmale · Answer

sorry, I don't often comment on answers unless I can see every bit of the work you did to obtain such answer.

hartnn · Answer

can you show your steps in finding cross product?
32i+j-14k does not seem to be correct.

mathmale · Answer

Kanwal32:  could you possibly look up and share the formula for cross product?  I believe I asked you to do this earlier.  How else would I know whether you're on the right track or not?

kanwal32 · Answer

by using determinants

mathmale · Answer

Well, y es,     but is it asking too much to ask you to share the actual formula y ou have in mind?

mathmale · Answer

What about the unit vectors i, j and k?  They must be part of your cross product.

kanwal32 · Answer

can i write deteminant

kanwal32 · Answer

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