JEE Main & Advanced
Mathematics
Vector Algebra
Question Bank
Modulus of vector Algebra of vectors
question_answer
The position vectors of P and Q are \[5\mathbf{i}+4\mathbf{j}+a\mathbf{k}\] and \[-\mathbf{i}+2\mathbf{j}-2\mathbf{k}\] respectively. If the distance between them is 7, then the value of a will be
A)5, 1
B)5, 1
C)0, 5
D)1, 0
Correct Answer:
A
Solution :
\[7=\sqrt{{{(5+1)}^{2}}+{{(4-2)}^{2}}+{{(a+2)}^{2}}}\Rightarrow a+2=\pm 3\] or \[a\,=-5,\,\,1.\]