Question

Which of the following vectors can be written as a linear combination of the vectors (1, 1, 2), (1, 2, 1) and (2, 1, 5)? (0.4,3.7,-1.5) (0.2,0) None of the selections is correct. All the selections are correct

Answer 1

Answer with explanation:

Let, A=[1,1,2]

B=[1,2,1]

C=[2,1,5]

⇒Now, Writing vector , A in terms of Linear combination of C and B

A=x B +y C

⇒[1,1,2]=x× [1,2,1] + y×[2,1,5]

1.→1 = x +2 y

2.→ 1=2 x +y

3.→ 2= x+ 5 y

Equation 3 - Equation 1

→3 y=1

$y=\frac{1}{3}$

$1=x+\frac{2}{3}\\\\x=1 -\frac{2}{3}\\\\x=\frac{1}{3}$

So, Vector A , can be written as Linear Combination of B and C.

⇒Now, Writing vector , B in terms of Linear combination of A and C

Now, let, B = p A+q C

→[1,2,1]=p× [1,1,2] +q ×[2,1,5]

4.→1= p +2 q

5.→2=p +q

6.→1=2 p +5 q

Equation 5 - Equation 4

-q =1

q= -1

→2= p -1

→p=2+1

→p=3

So, Vector B , can be written as Linear Combination of A and C.

⇒Now, Writing vector , C in terms of Linear combination of A and B

C=m A + n B

[2,1,5] = m×[1,1,2] + n× [1,2,1]

7.→2= m+n

8.→1=m +2 n

9.→5=2 m +  n

Equation 8 - Equation 7

n= -1

→m+ (-1)=2

→m=2+1

→m=3

So, Vector C , can be written as Linear Combination of A and B.

So, All the three vectors , A=[1,1,2],B=[1,2,1],C=[2,1,5] can be written as Linear combination of each other.

⇒≡But , the two vectors, (0.4,3.7,-1.5) (0.2,0),can't be written as Linear combination of each other as first vector is of order, 1×3, and second is of order, 1×2.