How many different groups of 3 students can be chosen from a class of 15 students?

"different groups" usually means a combination.

I'd also like to point out, most scientific calculator has an [ ₙCᵣ ] button for Combinations as well as [ ₙPᵣ ] for Permutations.

x^6

step-by-step explanation:

this is correct because:

x-6=0

0*x=0

so

x^6

no

step-by-step explanation:

2-7=-5

7-2=5

when you combing like terms for ech expression, 5 and -5. these numbers are not equal to each other.