Which expression is not equal to 1? sin θ csc θ cos θ sec θ tan θ cot θ sin θ cos θ

sin θ cos θ

Explanation:
Before we begin, remember that:
sec θ is the inverse of cos θ
csc θ is the inverse of sin θ
cot θ is the inverse of tan θ

let's check each of the given choices:
1- Option A:
sin θ csc θ = sin θ *  = 1
This option is incorrect

2- Option B:
cos θ sec θ = cos θ *  = 1
This option is incorrect

3- Option C:
tan θ cot θ = tan θ *  = 1
This option is incorrect

4- Option D:
sin θ cos θ
This expression cannot be further simplified. It is obvious that it is not equal to 1.
This option is correct.

Hope this helps :)