【证法9】(杨作玫证明)
做两个全等的直角三角形,设它们的两条直角边长分别为a、b(b>a),斜边长为c. 再做一个边长为c的正方形. 把它们拼成如图所示的多边形. 过A作AF⊥AC,AF交GT于F,AF交DT于R. 过B作BP⊥AF,垂足为P. 过D作DE与CB的延长线垂直,垂足为E,DE交AF于H.
∵ ∠BAD = 90º,∠PAC = 90º,
∴ ∠DAH = ∠BAC.
又∵ ∠DHA = 90º,∠BCA = 90º,
AD = AB = c,
∴ RtΔDHA ≌ RtΔBCA.
∴ DH = BC = a,AH = AC = b.
由作法可知, PBCA 是一个矩形,
所以 RtΔAPB ≌ RtΔBCA. 即PB =
CA = b,AP= a,从而PH = b―a.
∵ RtΔDGT ≌ RtΔBCA ,
RtΔDHA ≌ RtΔBCA.
∴ RtΔDGT ≌ RtΔDHA .
∴ DH = DG = a,∠GDT = ∠HDA .
又∵ ∠DGT = 90º,∠DHF = 90º,
∠GDH = ∠GDT + ∠TDH = ∠HDA+ ∠TDH = 90º,
∴ DGFH是一个边长为a的正方形.
∴ GF = FH = a . TF⊥AF,TF = GT―GF = b―a.
∴ TFPB是一个直角梯形,上底TF=b―a,下底BP= b,高FP=a +(b―a).
用数字表示面积的编号(如图),则以c为边长的正方形的面积为
【证法10】(李锐证明)
设直角三角形两直角边的长分别为a、b(b>a),斜边的长为c. 做三个边长分别为a、b、c的正方形,把它们拼成如图所示形状,使A、E、G三点在一条直线上. 用数字表示面积的编号(如图).
∵ ∠TBE = ∠ABH = 90º,
∴ ∠TBH = ∠ABE.
又∵ ∠BTH = ∠BEA = 90º,
BT = BE = b,
∴ RtΔHBT ≌ RtΔABE.
∴ HT = AE = a.
∴ GH = GT―HT = b―a.
又∵ ∠GHF + ∠BHT = 90º,
∠DBC + ∠BHT = ∠TBH + ∠BHT = 90º,
∴ ∠GHF = ∠DBC.
∵ DB = EB―ED = b―a,
∠HGF = ∠BDC = 90º,
∴ RtΔHGF ≌ RtΔBDC. 即.
过Q作QM⊥AG,垂足是M. 由∠BAQ = ∠BEA = 90º,可知 ∠ABE
= ∠QAM,而AB = AQ = c,所以RtΔABE ≌ RtΔQAM . 又RtΔHBT ≌
RtΔABE. 所以RtΔHBT ≌ RtΔQAM.即.
由RtΔABE ≌ RtΔQAM,又得QM = AE = a,∠AQM = ∠BAE.
∵ ∠AQM + ∠FQM = 90º,∠BAE + ∠CAR = 90º,∠AQM = ∠BAE,
∴ ∠FQM = ∠CAR.
又∵ ∠QMF = ∠ARC = 90º,QM = AR = a,
【证法16】(陈杰证明)
设直角三角形两直角边的长分别为a、b(b>a),斜边的长为c. 做两个边长分别为a、b的正方形(b>a),把它们拼成如图所示形状,使E、H、M三点在一条直线上. 用数字表示面积的编号(如图).
在EH = b上截取ED = a,连结DA、DC,
则 AD = c.
∵ EM = EH + HM = b + a , ED = a,
∴ DM = EM―ED = ―a = b.
又∵ ∠CMD = 90º,CM = a,
∠AED = 90º, AE = b,
∴ RtΔAED ≌ RtΔDMC.
∴ ∠EAD = ∠MDC,DC = AD = c.
∵ ∠ADE + ∠ADC+ ∠MDC =180º,
∠ADE + ∠MDC = ∠ADE + ∠EAD = 90º,
∴ ∠ADC = 90º.
∴ 作AB∥DC,CB∥DA,则ABCD是一个边长为c的正方形.
∵ ∠BAF + ∠FAD = ∠DAE + ∠FAD = 90º,
∴ ∠BAF=∠DAE.
连结FB,在ΔABF和ΔADE中,
∵ AB =AD = c,AE = AF = b,∠BAF=∠DAE,
∴ ΔABF ≌ ΔADE.
∴ ∠AFB = ∠AED = 90º,BF = DE = a.
∴ 点B、F、G、H在一条直线上.
在RtΔABF和RtΔBCG中,
∵ AB = BC = c,BF = CG = a,
∴ RtΔABF ≌ RtΔBCG.
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