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Sr nãy giờ quên mất câu này
A.
Ta có diện tích AMC < diện tích BMC vì AM < BM (gt)
B.
Ta có diện tích BNC < diện tích BMC vì NC < BM
Hình bạn tự vẽ vì cũng dễ mà
a) M điểm giữa của BC nên CM = MB
Tam giác ABM và tam giác ACM có : đáy CM = MB, chung đường cao tương ứng với đáy.
Nên S(ABM) = S(ACM)
b) S(ABC) = S(ABM) + S(ACM) mà S(ABM) = S(ACM)
Nên \(S\left(ABM\right)=\frac{1}{2}S\left(ABC\right)\)
1/2 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000% luob
Ta có Dien h tam giác ABM= 1/2x AMxBD. Dt tam giác BMC= 1/2xAMxCD. Do BD<DC nên Dt ABM < dt BMC