Question 337209
Use the FOIL method,
{{{(5sqrt(5)-15sqrt(7))(2sqrt(5)+6sqrt(7))=10sqrt(25)+30sqrt(35)-30sqrt(35)-90sqrt(49)}}}
{{{(5sqrt(5)-15sqrt(7))(2sqrt(5)+6sqrt(7))=10*5-90*7}}}
{{{(5sqrt(5)-15sqrt(7))(2sqrt(5)+6sqrt(7))=50-630}}}
{{{(5sqrt(5)-15sqrt(7))(2sqrt(5)+6sqrt(7))=-580}}}