设此圆弧对应的圆的半径是r,则r²=(11.7/2)²+(r-3)²求得r=7.20375 m ≈7.2m设这段弧长对应的圆心角的度数是α,则cosα=(r²+r²-11.7²)/(2r²)=-0.31893824820655344732227515763876...