(2) Complete $\mathrm{com}>,<\mathrm{ou}=$.
a) ${10}^3\le {10}^6$
c) 10000000 ${10}^7$
e) 0,000000
b) ${10}^{-5}\ge {10}^{-8}$
d) ${10}^{-2}\ge {10}^{-9}$
f) 0,000000
(3) Sendo $x=2,09\cdot {10}^{10}$ e $y=5,55\cdot {10}^{12}$, calcule $x+y$ e $x-y$.
(4) Sendo $x=8,1\cdot {10}^{23}$ e $y=4\cdot {10}^{15}$, calcule $x\cdot y$ e $x:y$.

Step 1 ：${10}^3\le {10}^6\Rightarrow \mathrm{com}>$

Step 2 ：${10}^7>10000000\Rightarrow \mathrm{com}>$

Step 3 ：${10}^{-5}\ge {10}^{-8}\Rightarrow \mathrm{com}<$

Step 4 ：${10}^{-2}\ge {10}^{-9}\Rightarrow \mathrm{com}<$

Step 5 ：x = 2.09 \cdot 10^{10}, y = 5.55 \cdot 10^{12}

Step 6 ：x + y = 2.09 \cdot 10^{10} + 5.55 \cdot 10^{12} = 5.550000209 \cdot 10^{12}

Step 7 ：x - y = 2.09 \cdot 10^{10} - 5.55 \cdot 10^{12} = -5.54999791 \cdot 10^{12}

Step 8 ：x = 8.1 \cdot 10^{23}, y = 4 \cdot 10^{15}

Step 9 ：x \cdot y = 8.1 \cdot 10^{23} \cdot 4 \cdot 10^{15} = 32.4 \cdot 10^{38}

Step 10 ：x : y = \frac{8.1 \cdot 10^{23}}{4 \cdot 10^{15}} = 2.025 \cdot 10^8

Step 11 ：$\boxed{{\displaystyle x+y=5.550000209\cdot {10}^{12}}}$

Step 12 ：$\boxed{{\displaystyle x-y=-5.54999791\cdot {10}^{12}}}$

Step 13 ：$\boxed{{\displaystyle x\cdot y=32.4\cdot {10}^{38}}}$

Step 14 ：$\boxed{{\displaystyle x:y=2.025\cdot {10}^8}}$