QLP+Q\frac{\mathrm{QL}}{\mathrm{P}+\mathrm{Q}}P+QQL
Q+LP+Q\frac{Q+L}{P+Q}P+QQ+L
QLP−Q\frac{\mathrm{QL}}{\mathrm{P}-\mathrm{Q}}P−QQL
Q−LP+Q\frac{Q-L}{P+Q}P+QQ−L