Convert into a decimal number

Question

How can we convert in $\mathbb{Q}$ the inverse of $1{,}2^2$ (i.e the number $\frac{1}{ 1{,}2^2}$) into a decimal number?

Also how could we show that with the complex multiplication $\cdot$ then $(G, \cdot)$ is a commutative group?

Could you give me a hint?

Answer 1

Just a guess, your question isn't very clear so I'll guess you're asking us to convert $1 \over 1.2^2$ into a decimal number.

$1 \over 1.2^2$

$=$ $1 \over 1.44$

$=$$100 \over 100$$\div$$144 \over 100$

$=$$100 \over 100$$\times$$100 \over 144$

$=$$100 \over 1$$\times$$1 \over 144$

$=$$100 \over 144$

$=$$0.69\overline4$