插入公式

a2+b2=c2a^2 + b^2 = c^2

a0a \ne 0时,ax2+bx+c=0ax^2 + bx + c = 0有两个根: (5分)

       

x=b±b24ac2a\displaystyle {x = {-b \pm \sqrt{b^2-4ac} \over 2a}}

Double angle formula for Cosines

cos(θ+φ)=cos(θ)cos(φ)sin(θ)sin(φ)\displaystyle {\cos \left( {\theta + \varphi } \right) = \cos \left( \theta \right)\cos \left( \varphi \right) - \sin \left( \theta \right)\sin \left( \varphi \right)}