√20а+√45а-2√5а

To simplify the expression \( \sqrt{20a} + \sqrt{45a} - 2\sqrt{5a} \), we first simplify each square root term:

1. Simplify \( \sqrt{20a} \): \[ \sqrt{20a} = \sqrt{4 \cdot 5 \cdot a} = \sqrt{4} \cdot \sqrt{5} \cdot \sqrt{a} = 2\sqrt{5a} \]

2. Simplify \( \sqrt{45a} \): \[ \sqrt{45a} = \sqrt{9 \cdot 5 \cdot a} = \sqrt{9} \cdot \sqrt{5} \cdot \sqrt{a} = 3\sqrt{5a} \]

Now we can substitute these simplified forms back into the expression: \[ \sqrt{20a} + \sqrt{45a} - 2\sqrt{5a} = 2\sqrt{5a} + 3\sqrt{5a} - 2\sqrt{5a} \]

Next, we combine the like terms: \[ (2\sqrt{5a} + 3\sqrt{5a} - 2\sqrt{5a}) = (2 + 3 - 2)\sqrt{5a} = 3\sqrt{5a} \]

Thus, the simplified expression is: \[ \boxed{3\sqrt{5a}} \]