$$a^2 - b^2 = (a + b)(a - b)$$ $$a^3-b^3=(a-b)(a^2+ab+b^2)$$ $$a^3+b^3=(a+b)(a^2-ab+b^2)$$ $$(a-b)^2=a^2-2ab+b^2$$ $$(a+b)^2=a^2+2ab+b^2$$ $$(a-b)^3=a^3-3a^2b+3ab^2-b^3$$ $$(a+b)^3=a^3+3a^2b+3ab^2+b^3$$ $$(a+b+c)^2=a^2+b^2+c^2+2ab+2ac+2bc$$ $$(a+b)^2+(b+c)^2+(a+c)^2=2a^2+2b^2+2c^2+2ab+2bc+2ac $$$$\sqrt{a^2 + b^2} = \sqrt{\sum_{i=1}^n x_i^2}$$ $$\sqrt{ab}=\sqrt{a}*\sqrt{b}$$ $$ax^2+bx+c=0(a!=0) x = \frac{-b \pm \sqrt{b^2-4ac}}{2a} $$$$两点坐标(x_1,y_2),(x_2,y_2) d=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2} 中点p的坐标为\frac{(x_1+x_2)}{2},\frac{(y_1+y_2)}{2} $$$$\pi = \lim_{n\to\infty} 4\sum_{k=1}^n \frac{(-1)^{k+1}}{2k-1} $$$$圆柱面积2\pi rh+2\pi r^2$$ $$圆面积 \pi r^2$$ $$正方形面积l^2$$ $$球体积\frac{4}{3}\pi r^3$$