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Primary school students' mathematical thinking training, the fifth grade, the second volume, the first lecture, the answer to the fourth question
Let s △ PCD = X, s △ PBC = Y, s △ PAC = Z.
S△PAB+S△PCD=S△PAD+S△PBC=S parallelogram /2
Namely: 5+x=2+y y-x=3.
S △ ACD = S △ PCD+S △ Pad+S △ PAC = S △ PAB+S △ PBC-S △ PAC = S △ ABC = S parallelogram /2