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ngothithanhthu
2 năm trước
Cho hình thang ABCD có ∠B= ∠C=90 độ. Các đường chéo vuông góc với nhau tại Q. a) C/m $\frac{1}{AB^{2}}$ -$\frac{1}{CD^{2}}$=$\frac{1}{QB^{2}}$-$\frac{1}{QC^{2}}$ b) Các đường trung tuyến QE và BF của Δ BQC vuông góc với nhau tại G, biết BQ= $\sqrt[2]{6}$ cm. Tính BC.
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