# Vector perpendicular to the plane

1. May 9, 2010

### xstetsonx

For what value of a is the vector v=(-2,1,a) perpendicular to the plane z=6x-3y+4?

i looked the book and my teacher's solution they are different so i just want to make sure i did this right.....

Vector v is perpendicular to the plane if it is parallel to the plane’s normal vector. A vector which is normal (= perpendicular) to the plane is n=(6,-3, 4) Hence, v parallel n if their coordinates are proportional, i.e. −2/6=1/3=a/4, therefore a=4/3

can someone correct me if i am wrong?????????????PLZ

2. May 10, 2010

You got one component of the normal vector wrong.

3. May 10, 2010

### xstetsonx

how??? z=6x-3y+4 don't u just take the coefficient and that is your normal vector?

4. May 10, 2010

### Gigasoft

Do you see a 4z in your equation?

5. May 10, 2010

### xstetsonx

aw crap so is it -1 then?

Last edited: May 10, 2010
6. May 10, 2010

### xstetsonx

since i have two vectors why can't i do Vector1 . Vector2=0?
since the dot product says a.b=0 is perpendicular to each other?