[tex]\displaystyle\bf\\\sqrt{(35+10)\cdot(35-10)} =\sqrt{45\cdot 25}=\sqrt{9\cdot 5\cdot25}= \\\\=\sqrt{3^{2} \cdot 5\cdot5^{2}} =3\cdot 5\cdot \sqrt{5} =15\sqrt{5}[/tex]