The liquidity pool will offer you a conversion rate, in our case, 3,000 DAI (y) for 1 ETH (x). When you supply the 3,000 DAI to the pool and remove 1 ETH, it will have a higher supply of DAI and a smaller supply of ETH. This action causes the price of ETH to rise as k is constant. In other words, you are using your DAI to buy ETH. As more ETH leaves the pool, its price in comparison to DAI rises.