>>648
　dy/du = 1 + cos(u),
　dy/dx = -tan(u)^2 = -{1-cos(u)^2}/cos(u)^2,
辺々割って
　dx/du = -cos(u)^2 /{1-cos(u)} = 1 + cos(u) -1/{1-cos(u)},
uで積分して
　x = u + sin(u) + cot(u/2),
　y = u + sin(u),


>>665
　f(x) = 7cos(x) -x とおくと
　f(π/3) = (7/2) -(π/3) >0,
　f(π/2) = -(π/2) <0,
　f(3π/2) = -(3π/2) <0,
　f(2π) = 7 -2π >0,