√5a - 3√20a + √125a = √5a - 3√4*5a + √25*5a = √5a - 3*2√5a + 5√5a = √5a - 6√5a + 5√5a = 6√5a - 6√5a = 0
√5a - 3√20a + √125a = √5a - 3√4*5a + √25*5a = √5a - 3*2√5a + 5√5a = √5a - 6√5a + 5√5a = 6√5a - 6√5a = 0