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Consider the basis B of R2 consisting of vectors


5

-6

and

-2

-2


Find x in R2 whose coordinate vector relative to the basis B is


[x]B = [-6]

[ 2 ]

Verified Answer :

The idea is to find a linear combination a_1(5, -6) + a_2(-2, -2) = (-6, 2)

It boils down to a system of equations:
Take the augmented matrix:

[5−6−2−2−62]
Reduced form:
[1001−8111311]

-(8/11)(5, -6) + (13/11)(-2, -2) = (-6, 2)

Answer:  The required vector x is

\(x=\begin{bmatrix}-\dfrac{8}{11}\\ \dfrac{13}{11}\end{bmatrix}\).

Step-by-step explanation:  Given that a basis B of R² consists of vectors (5, -6) and (-2, -2).

We are to find the vector x in R² whose co-ordinate vector relative to the basis B is \(\begin{bmatrix}-6\\ 2\end{bmatrix}\).

Let us consider that a, b are scalars such that

\(a(5,-6)+b(-2,-2)=(-6,2)\\\\\Rightarrow (5a-2b,-6a-2b)=(-6,2)\\\\\Rightarrow 5a-2b=-6~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~(i)\\\\-6a-2b=2~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~(ii)\)

Subtracting equation (ii) from equation (i), we get

\((5a-2b)-(-6a-2b)=-6-2\\\\\Rightarrow 11a=-8\\\\\Rightarrow a=-\dfrac{8}{11}\)

and from equation (i), we get

\(5\times\left(-\dfrac{8}{11}\right)-2b=-6\\\\\\\Rightarrow 2b=-\dfrac{40}{11}+6\\\\\\\Rightarrow 2b=\dfrac{26}{11}\\\\\\\Rightarrow b=\dfrac{13}{11}.\)

Thus, the required vector x is

\(x=\begin{bmatrix}-\dfrac{8}{11}\\ \dfrac{13}{11}\end{bmatrix}\).