Amazon’s acquisition strategy has become evident after its two latest deals, according to DA Davidson. The e-commerce giant announced last week it was acquiring Roomba-maker iRobot for $1.7 billion. The news followed last month’s $3.9 billion acquisition of primary health-provider One Medical . In both cases, Amazon is following its historical approach of “build first, buy second,” DA Davidson’s senior research analyst Tom Forte wrote in a note. In other words, Amazon is acquiring companies after it has already started building those businesses within the company. It’s the same approach Amazon used with Whole Foods, Zappos and MGM, Forte noted. The company, which had $60.71 billion in cash and investments on hand in the second quarter, is paying all cash for its latest acquisitions. “That suggests to us management believes its shares are undervalued, at current levels, which we find…