Cutting angle help

I have a 4x4 post in the ground and need to cut a 2 x 8 at an angle to make it flush with the 4x4. Here is a picture looking down the 4x4 to the 2x8.

The way the board is resting against the 4x4 it creates an angle that is clear in this photo. If I measure that angle and cut the 2x8 at that angle will it allow me to attache the 2x8 flush to the left side of the 4x4?

If not how do I figure the correct angle with wasting time cutting and trying over and over.

The 2x8 is not straight across as that would of been easy but to attach it to the other side. I have to angle it.

Thanks in advance for your help

 

Step back and take another photo including the 4x4. Your question is not clear.

 

Let your 2x8 board be propped on the outside of both the post you have there and the other post that will be attached to on the opposite end to the left. Have someone hold the board in place, or tack it up with a brad or two. Then take a scrap piece of lumber and lay it flush with the left side of the 4x4 and scribe a line onto your 2x8 stock. The scribed line will very much mimic the shadow line in your picture. Do the same for the post on the left. You now have a perfect fit if you cut both those lines.

 

A sliding T-Bevel can come in handy for this type of cut.



Johnson T-Bevel-B75 - The Home Depot

 

When the 2x6 swings in to the flush position, the angle will change from from what it is when the 2x8 is on the outside of the 4x4.

 

Not if you side saddle both connection points at both ends of the board before marking. Then both angles will be correct.

 

Thank you for all your help. I have attached a few more photos as was asked by one person but I think your suggestions are very helpful. If it will just stop raining I may be able to get back out there and finish this silly thing.