[tex]\dfrac{1}{2} \cdot 5 \cdot \sqrt{42,35} =\dfrac{5}{2} \cdot \sqrt{42\dfrac{35}{100} } =\dfrac{5}{2} \cdot \sqrt{\dfrac{4235}{100} }=\dfrac{5}{2} \cdot \sqrt{\dfrac{121\cdot 35}{100} }=\dfrac{5}{2} \cdot \sqrt{\dfrac{11^{2} \cdot 35}{10^{2} } }=\dfrac{5}{2} \cdot \dfrac{\sqrt{11^{2} } \cdot \sqrt{35} }{\sqrt{10^{2} } } =\dfrac{5}{2} \cdot \dfrac{11\cdot \sqrt{35} }{10} =\dfrac{11\cdot \sqrt{35} }{4} =\dfrac{11}{4} \sqrt{35} =2\dfrac{3}{4} \sqrt{35} =2,75\sqrt{35}[/tex]
