ABCD is a rhombus. Prove that AB² + BC² + CD²+ DA² = AC² + BD²

Since ABCD is rhombus. So we have;
AB = BC = CD = AD
so we can write ${\mathrm{AB}}^2+{\mathrm{BC}}^2+{\mathrm{CD}}^2+{\mathrm{DA}}^2 = 4{\mathrm{BC}}^2$

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