a)

$16=4\cdot 4=4^2=\left(-4\right)\cdot \left(-4\right)={\left(-4\right)}^2$

4 lub -4

b)

$900=30\cdot 30={30}^2=\left(-30\right)\cdot \left(-30\right)={\left(-30\right)}^2$

30 lub -30

c)

$81=9\cdot 9=9^2=\left(-9\right)\cdot \left(-9\right)={\left(-9\right)}^2$

9 lub -9

d)

$1=1\cdot 1=1^2=\left(-1\right)\cdot \left(-1\right)={\left(-1\right)}^2$

e)

$\frac{1}{4}=\frac{1}{2}\cdot \frac{1}{2}={\left(\frac{1}{2}\right)}^2=\left(-\frac{1}{2}\right)\cdot \left(-\frac{1}{2}\right)={\left(-\frac{1}{2}\right)}^2$

$\frac{1}{2}\text{lub}\left(-\frac{1}{2}\right)$

f)

$\frac{4}{49}=\frac{2}{7}\cdot \frac{2}{7}={\left(\frac{2}{7}\right)}^2=\left(-\frac{2}{7}\right)\cdot \left(-\frac{2}{7}\right)={\left(-\frac{2}{7}\right)}^2$

$\frac{2}{7}\text{lub}\left(-\frac{2}{7}\right)$

g)

$0,36=0,6\cdot 0,6={0,6}^2=\left(-0,6\right)\cdot \left(-0,6\right)={\left(-0,6\right)}^2$

0,6 lub -0,6

h)

1,21=1,1*1,1=1,1^2=(-1,1)*(-1,1)=(-1,1)^2

1,1 lub -1,1

i)

$3\frac{1}{16}=\frac{49}{16}=\frac{7}{4}\cdot \frac{7}{4}={\left(\frac{7}{4}\right)}^2=\left(-\frac{7}{4}\right)\cdot \left(-\frac{7}{4}\right)={\left(-\frac{7}{4}\right)}^2$

$\frac{7}{4}\text{lub}\left(-\frac{7}{4}\right)$

j)

$11\frac{1}{9}=\frac{100}{9}=\frac{10}{3}\cdot \frac{10}{3}={\left(\frac{10}{3}\right)}^2=\left(-\frac{10}{3}\right)\cdot \left(-\frac{10}{3}\right)={\left(-\frac{10}{3}\right)}^2$

$\frac{10}{3}\text{lub}\left(-\frac{10}{3}\right)$