4x-5/7=51/7;t0]:l6x,p9O9A;B(r*b
算式：提示9M-x;d(u-X:X*R4p0D.s;t0]:l6x,p9O9A;B(r*b
=)i5B1x5K7I6l3S,e;t0]:l6x,p9O9A;B(r*b