[tex] \frac{a+b}{2}-media_{aritmetica} \\
a=8-3 \sqrt{7}+ \frac{1}{2}(3+ \sqrt{7} )^2=8-3 \sqrt{7}+ \frac{1}{2}(9+6 \sqrt{7}+7)= \\ =8-3 \sqrt{7}+ \frac{1}{2}(16+6 \sqrt{7} )=8-3 \sqrt{7}+8+3 \sqrt{7}=16 \\
b=24 \\
m_{a}= \frac{a+b}{2}= \frac{16+24}{2}= \frac{40}{2}=20 [/tex]
