vectors????pls answer with an valid explanation to collect 10 points.?

Question

1) If vector A = 5i +7j -3k , vector B =2i +2j -ck r perpendicular to each other find the value of c?
2)Two vectors start from origin and end at (1,3,4)and(1,2,3).whats their cross product?
3)A vector Fa is along positive X-axis.If it s vector product with Fb is zero than Fb is what??? Answer in unit vectors
4) what will bethe angle between vectors -2i +3j+k and -i +2j +2k
5)Three vectors A,B and C satisfy the relation A.B=0 , A.C=0 than vector A will be parallel what????

Answer 1

question 1:
since its given A,B are ppdeclr their dot product must be 0

on finding the dot product ....
we get 10+14+3c = 0

ie c= --8

question2
u gotta know how to find the determinant to solve this

(1,3,4)=i+3j+4k and (1,2,3)=i+2j+3k

find det
| i j k |
| 1 3 4|
| 1 2 3|

i m too lazy find urself

question3
cross profuct is zero ie angle bween Fa and Fb is 0 or 180degress . Fb=+i or -i

question4
just find the dot product dude
let "x" be the angle

(|-2i+3j+k|) *(|-i+2j+2k|)*cos(x) = 2+6+2

ie root(4+9+1)*root(1+4+4)*cos(x)=10
ie root(14*9)*cos(x)=10
ie cos(x)=10/root(126)
ie x=cos(inv)[10/root(126)]

question5:
I didnt understand But may be (BxC)

POST THESE KINDA QUESTIONS IN MATH SECTION

Answer 2

How about asking each question separately so that I can earn 10 points for each question rather than all 5?