sin（X+19π/6）+sin²（π/3-X）=sin（X+3π+π/6）+sin²（π/2-π/6-X）=sin（X+π+π/6）+cos²（π/6+X）=-sin（X+π/6）+cos²（π/6+X）=-2/3+1-sin²（π/6+X）=1/3-(2/3)²=1/3-4/...