Question

# If two vectors whose direction ratios are 1,2,3 and -k,2,1 are perpendicular to each other then, a) k=7 b) k=4 c) k=3 O d) k=6 me especially since we had be 1 poir 82) I don't know why he turned friends for so long.​

Answer 1

(a)k=7

Explanation:

We are given that

Two vectors whose direction ratios are 1,2,3 and -k,2,1.

Let

`a_1=1,b_1=2,c_1=3`

`a_2=-k,b_2=2,c_2=1`

We have to find the value of k.

We are given that two vectors are perpendicular to each other.

We know that two vectors are perpendicular to each other then

`a_1a_2+b_1b_2+c_1c_2=0`

Substitute the values

`1(-k)+2(2)+3(1)=0`

`-k+4+3=0`

`-k+7=0`

`\implies k=7`

Hence, option a is correct.