Math  /  Algebra

QuestionExample 5.2.1. Let T(x1,x2,x3)=(x1x2,2x1+2x2+x3,x1+x2+x3)T\left(x_{1}, x_{2}, x_{3}\right)=\left(x_{1}-x_{2},-2 x_{1}+2 x_{2}+x_{3},-x_{1}+x_{2}+x_{3}\right) and b=(1,0,1)\vec{b}=(1,0,-1). Determine whether bT(R3)\vec{b} \in T\left(\mathbb{R}^{3}\right).

Studdy Solution

STEP 1

What is this asking? Is the vector (1,0,1)(1, 0, -1) in the range of the transformation TT?
In simpler terms, can we find some input vector that, when transformed by TT, produces (1,0,1)(1, 0, -1)? Watch out! Don't mix up the domain and range!
We're looking for an input vector in R3\mathbb{R}^3, not an output vector.

STEP 2

1. Set up the system of equations
2. Solve the system

STEP 3

We want to find out if there exist x1x_1, x2x_2, and x3x_3 such that T(x1,x2,x3)=(1,0,1)T(x_1, x_2, x_3) = (1, 0, -1).

STEP 4

Remember, T(x1,x2,x3)T(x_1, x_2, x_3) is defined as (x1x2,2x1+2x2+x3,x1+x2+x3)(x_1 - x_2, -2x_1 + 2x_2 + x_3, -x_1 + x_2 + x_3).

STEP 5

So, we need to see if we can solve: x1x2=1x_1 - x_2 = 1 2x1+2x2+x3=0-2x_1 + 2x_2 + x_3 = 0x1+x2+x3=1-x_1 + x_2 + x_3 = -1

STEP 6

From the first equation, we get x1=1+x2x_1 = 1 + x_2.
We did this so we can substitute it into the other equations and get rid of x1x_1!

STEP 7

Substituting into the second equation, we have 2(1+x2)+2x2+x3=0-2(1 + x_2) + 2x_2 + x_3 = 0.

STEP 8

This simplifies to 22x2+2x2+x3=0-2 - 2x_2 + 2x_2 + x_3 = 0, which means x3=2x_3 = 2.
Boom! We found x3x_3!

STEP 9

Now, substitute x1=1+x2x_1 = 1 + x_2 and x3=2x_3 = 2 into the third equation: (1+x2)+x2+2=1-(1 + x_2) + x_2 + 2 = -1.

STEP 10

This simplifies to 1x2+x2+2=1-1 - x_2 + x_2 + 2 = -1, which gives us 1=11 = -1.
Whoa, that's not right!

STEP 11

This contradiction tells us there's no solution to the system of equations.
There are no values of x1x_1, x2x_2, and x3x_3 that satisfy all three equations simultaneously.

STEP 12

Since there's no solution to the system, the vector (1,0,1)(1, 0, -1) is *not* in the range of the transformation TT.
So, bT(R3)\vec{b} \notin T(\mathbb{R}^3).

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