Question 16: Let ABC be a triangle, let AD be perpendicular to BC and D, then BD+DC=BC, AB? -BD？ =AC？ DC？ , from here, DC? =3-3BD？
a b+ 2BC = a b+ 2(BD+DC)= 2BD+2BD+2DC = 4BD+2DC
Suppose BD=X, AB+2BC=4X+2* radical sign (3-3X? ), let X=sin x, then =4sinx+2* radical number 3*cosx=4*( 1/2sinx+ (radical number 3)/2 *cosx)=sin.
Get 2 and root 7.