Answers

2015-11-01T13:38:00+05:30
Acosα -bsinα = x
asinα - bcosα = y

squaring both the equations and adding

a²cos²α + b²sing²α -2absinαcosα = x²
a²sin²α + b²cos²α + 2absinαcosα = y²

a² + b² = x² + y²
thus proved.
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