On the 40th and the 80th you will receive both a free beverage and a free appetizer. You can find this by simply finding the multiples of both number up to 100 (or a little more than 100) to find out on which dates you'd get bothe an appetizer and beverage for free. Here are the multiples of both, to prove this answer.
- 8: 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, 104.
- 10: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100.
Thus making 40 and 80 the answers. I hope this helps!
He made a mistake in step #2. It seemed to be a trivial mistake because it involved signs, but it still had a great impact. Since step#2, his solution was already wrong.
Instead of
(-1)²-4(2)(-6) = 1 + 48 = 49
What he did is
(-1)²-4(2)(-6) = -1 + 48 = 47
The domain is the set of allowed x inputs, or x coordinates of a function. In this case, any point on the curve has an x coordinate that is 4 or smaller.
Therefore, the domain is the set of numbers x such that
To write this in interval notation, we would write
This interval starts at negative infinity and stops at 4. We exclude infinity with the curved parenthesis and include 4 with the square bracket.
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The range is the set of possible y outputs. Every point on this curve has a y coordinate that is either 0 or it is larger than 0.
The range is the set of y values such that 
In interval notation, it would be written as
This time we start at 0 (including this endpoint) and "stop" at infinity
note: we always use curved parenthesis at positive or negative infinity because we cannot reach either infinity