Shannon was born on 12/21/1982. How many eight digit codes could she make using the digits in her birthday?

Explanation:

Ignoring the slashes, there are 8 digits here. If we could tell those '1's and '2's apart, then we'd have 8! = 40,320 different codes. The exclamation mark indicates a factorial.

However, the '1's and '2's are indistinguishable. We have to divide by a!*b! = 3!*3! = 6*6 = 36 to account for this.

The a! = 3! = 6 is from the fact we have 3 copies of '1'.

The b! = 3! = 6 is from the fact we have 3 copies of '2'

Dividing by 36 gets us (40,320)/36 = 1120

you would use (d.) the law of cosines or a^2 = b^2 + c^2 – 2bc(cos a)

, b^2 = a^2 + c^2 – 2ac(cos b), or c^2 = a^2 + b^2 - 2ab(cos c). you wouldn't use b. the law of sines as it is mostly effective when 1side and 2angles are given. a and c aren't the answer for they are the improper versions of the law of cosines. hope this is .