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# 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.​

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lublana

Answer:

(a)k=7

Step-by-step explanation:

We are given that

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

Let

[tex]a_1=1,b_1=2,c_1=3[/tex]

[tex]a_2=-k,b_2=2,c_2=1[/tex]

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

[tex]a_1a_2+b_1b_2+c_1c_2=0[/tex]

Substitute the values

[tex]1(-k)+2(2)+3(1)=0[/tex]

[tex]-k+4+3=0[/tex]

[tex]-k+7=0[/tex]

[tex]\implies k=7[/tex]

Hence, option a is correct.

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