(sin )﹣2+(sin
)﹣2=
×1×2;
(sin )﹣2+(sin
)﹣2+(sin
)﹣2+sin(
)﹣2=
×2×3;
(sin )﹣2+(sin
)﹣2+(sin
)﹣2+…+sin(
)﹣2=
×3×4;
(sin )﹣2+(sin
)﹣2+(sin
)﹣2+…+sin(
)﹣2=
×4×5;
…
照此规律,
(sin )﹣2+(sin
)﹣2+(sin
)﹣2+…+(sin
)﹣2=.