# Equivalence relations problem #2 (alg)

1. Jan 24, 2006

### Pearce_09

R = the real numbers

A = R x R; $$(x,y) \equiv (x_1,y_1)$$ means that
$$x^2 + y^2 = x_1^2 + y_1^2;$$ B= {x is in R | x>= 0 }

Find a well defined bijection sigma : $$A_\equiv -> B$$

like the last problem, I just cant seem to find the right way to solve this??

2. Jan 24, 2006

### matt grime

hint 1 x^2+y^2 is a positive real number.

hint 2 What is an equivalence class under this relation, think geometrically.

hint 3 radius.

3. Jan 26, 2006

### fourier jr

did you get it?

4. Jan 26, 2006

### Pearce_09

ya i did thanks fourier

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