
mAB=mAD⇒t1+t22=at12−α2a(t1−t3)⇒at12−α=a{t12−t1t3+t1t2−t2t3}⇒α=a(t1t3+t2t3−t1t2)AM=∣2a(t1−t3)∣,BN=∣2a(t2−t3)∣,CD=at32−α CD=at32−a(t1t3+t2t3−t1t2)=at32−t1t3−t2t3+t1t2=a∣t3(t3−t1)−t2(t3−t1)∣CD=a∣(t3−t2)(t3−t1)∣(CDAM⋅BN)2={a(t3−t2)(t3−t1)2a(t1−t3)⋅2a(t2−t3)}216a2=16×49=36