Which expression is equivalent to (sin x + 1)(sin x − 1)?

Keep in Mind the trigonometric Identity to solve the problem

sin²x+cos²x=1

cos²x= 1 - sin²x

Now, (Sin x -1)× (Sin x +1)

= (Sin²x-1²)→→→Used the Identity, (a-b)(a+b)=(a²-b²)

= Sin²x-1

= - (1-sin²x)

= -Cos²x