若a=ba=ba=b,则a±c=b±ca \pm c = b \pm ca±c=b±c 若a=ba=ba=b,则ac=bcac = bcac=bc 若a=ba=ba=b 且 c≠0c \ne 0c≠0,则a⋅1c=b⋅1ca \cdot \frac{1}{c} = b \cdot \frac{1}{c}a⋅c1=b⋅c1