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How to do 20 1 1 College Entrance Examination Mathematics 12 16?
12 choose b, and the intersection point is symmetrical about X= 1, so it is 4.

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.