HSBC Holdings Plc said first-half profit at its investment bank dropped 5.6 percent as legal expenses overshadowed an increase in revenue from foreign exchange and equities. Pretax profit in global banking and markets, the division that houses the firm’s trading units, fell to $4.75 billion from $5.03 billion in the year-earlier period, the bank said as it reported results Monday. Revenue rose 10 percent to $10.1 billion at the division, paced by a 24 percent increase at its foreign exchange unit, the biggest driver of its markets business, and a 75 percent surge in equities income.