Question

np3 =6 × nC2 find n​

Answer 1

solve for n

n(n-1)(n-2)/2!(n-2)! = 6

=

n(n-1)/2 = 6

n^2-n+12=0

factor

(n+3)(n-4)=0

n=-3,4 cant be negative so n=4

I dont know why n cant equal a negative number? I think there was another unit in my math class where x couldnt be negative (I cant remember)

I made up that question so so I dont have trouble solving it, I just want to know why it cant be negative.