If the negative square root is found to be one of your solutions, then that is indicative of a pair of imaginary roots (the imaginary i). According to the conjugate rule, if you have one solution that is imaginary, you will have another but with the opposite sign. For example, if a solution to a quadratic is found to be 2 - i, then its conjugate, 2 + i is also a solution. They will ALWAYS go in pairs. Same thing with radical solutions. If one solution is found to be 
then 
will also be a solution.
In all right triangles, the ratio between a leg and the hypothenuse is the sine of the angle opposite to the leg.
So, in your case, we have
In order to find XY, we have
So, the ratio for the sine is
The value of 8 is Hundred Thousand
Let us assume the total amount of meal charge paid by Michael without tax = x
Then
Amount paid to the waiter by Michael = 15x/100
Sales tax paid by Michael = 5x/100
Now we get the equation as
x + (5x/100) + (15x/100) = 18
(100x + 5x + 15x)/100 = 18
120x/100 = 18
120x = 1800
x = 1800/120
= 180/12
= 15 dollars
So the amount paid by Michael for the meal before tax and tip is $15. I hope the procedure is clear enough for you to understand.
