S=1/2absinC=1/2sin10sin50sin70=1/4*sin10cos10sin50cos20/cos10=1/4sin20cos20sin50/cos10=1/8sin40cos40/cos10=1/16sin80/sin80=1/16
选择C
S=1/2absinC=1/2sin10sin50sin70=1/4*sin10cos10sin50cos20/cos10=1/4sin20cos20sin50/cos10=1/8sin40cos40/cos10=1/16sin80/sin80=1/16
选择C