Ive got part one i need part two

Which equations represents circles that have a diameter of 12 units and a center that lies on the y-axis? check all that apply

Ascientist wants to use a model to present the results of his detailed scientific investigation. why would a model be useful? a )because the model makes the concepts easier to understand b) because the model is easy to put together and to use c) because the model prevents other scientists from asking questions d) because the model requires the audience to pay full attention to it i don't know what to choose because between a and d a is much more likely than d because it only wants to get the attention of the audience. i'm confuse.

Need match the functions with correct transformation. f(x) = -3x f(x) = |x-1|+3 f(x) = √(x+3) 1/2x² f(x) = (x+1)²-3 4|x| 1. compress by a factor of 1/2 2. stretch by a factor of 4 3. shift to the left 3 4. shift to the left 1 5. shift up 3 6. reflection