Hello. Am making a deck and getting hung up on geometry and woodcutting.

The way the stairs are going, I have to have two pieces of wood at a 130
degree angle from each other



*******
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*****B** A
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I tried to depict it above. What manner of power tool does one use to cut
the slanted board coming down? The edge (B) is cut beyond 45 degree which is
what my skil saw and my miter saw go to. Miter box is same way. Hand saw
sucks for this (These are 2" x 8" deck boards), because I can't cut it
straight enough.
Bottom line question: how do I cut an angle greater than 45 degrees??

Thanks in advance for any help.

John