A^2 +a-6. You use the method of foiling where you multiply the first two terms, the the outside terms, the inside terms, then the last terms. You would do a•a, then a•-2 the a•3 then 3•-2. You would get a^2 -2a +3a -6. Then combine like terms to get your answer.
C. would be the correct device to use in trials.
But the actual probability is:
(1-1/4)^5
243/1024
(about 23.73% chance none of the five chose vanilla)
They are equivalent because they have the same numbers and when you do the math it give 96 for both of them
Check the picture below.
so, as you see there, those radius make out an "equilateral triangle", and as you know, all angles in an equilateral triangle are 60° each.
now, if we make out the other equilateral triangle underneath that one, and add up the angles making out ∡CBD, you'd get, yes, you guessed it.