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Previous Year Question (PYQs)



Let $G = \frac{R}{{0}}$ and $H = {-1, 1}$ be groups under the multiplication. Then, the map $\phi : G \to H$ defined by $\phi(x) = \frac{x}{|x|}$ is





Solution

$\phi(x) = \frac{x}{|x|}$ gives the sign of $x$.

If $x > 0$, then $\phi(x) = 1$

If $x < 0$, then $\phi(x) = -1$

Also,

$\phi(xy) = \phi(x)\phi(y)$

So, it is a homomorphism.

It is onto because both $1$ and $-1$ are obtained.

It is not one-one because many positive numbers map to $1$, and many negative numbers map to $-1$.


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