Today we studies the Double Angle ID's: sin(2A)=2sinAcosA and cos(2A)=cos^2A-sin^2A. Once you solve for both sin(2A) and cos(2A), you can solve for tan(2A)=sin(2A)/cos(2A). It's important to know that for that the 2 in 2 sinAcosA isn't the same as the 2 in its equivalent sin(2A). Its derived from the sum of the 2A represented in the equation 2(sinAcosA).