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beetle2
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Homework Statement
The problem is as follows:
Let f : R^2 map to R^2 be rotation through an angle of theta radians about the origin.
Prove that f is an isomorphism.
Homework Equations
Let f :[itex] R^2 \rightarrow R^2 [/itex]
The Attempt at a Solution
I know that the rotation can be expressed as the 2 x 2 matrix
cos(theta) -sin(theta)
Sin(theta) cos(theta)
And its inverse I believe is
cos(theta) -sin(theta)
-sin(theta) cos(theta)
Do I first show that f :[itex] R^2 \rightarrow R^2 [/itex] is a linear transformation
by closure of addition and scaler multiplication by using x,y elements of R2 and some scaler k
Say let the 2x2 matrix:
cos(theta) -sin(theta)
Sin(theta) cos(theta) = A
We need to show
A(x+y) = A(x) + A(y)
cos(theta)x -sin(theta)y = cos(theta)x + -sin(theta)y = cos(theta)x -sin(theta)y
sin(theta)x cos(theta)y sin(theta)x + cos(theta)y sin(theta)x cos(theta)y
likewise
A(kx+ky) = K A(x+y)
cos(theta)kx + -sin(theta)ky = cos(theta)xk -sin(theta)yk
sin(theta)kx + cos(theta)ky sin(theta)xk cos(theta)yk
Do I need to use the inverse or can I use an assumption some how?
Basically I’m having trouble with knowing how to prove that the function is 1-1 and surgective.
As well as constructing the proof logically and stating the proof clearly.
If anyone can help that would be great.
Regards