B2C2=1/2BC=1/2a
B1C1=1/2B2C2=1/4BC=1/4a
B3C3=(BC+B2C2)/2=(a+1/2a)/2=3/4a
B1C1+B2C2+B3C3=1/2a+1/4a+3/4a=1.5a