81 is divisible by?

1. 3
2. 4
3. 6
4. 8

For what values of b will f(x)= logbx be a decreasing function? (16 )

What are the domain and range of the function? f(x) = -4 (sqrt)x

Which of the expressions (on the photo document i inserted) together represent all solutions to the following equation? 8cos(12x)+4=-4 *the answer should be in degrees.* > i would like for someone to explain the process to find the solutions for this.