1.

( a \operatorname sin \theta - b \operatorname cos \theta ) ^ 2 %2B ( a \operatorname cos \theta %2B b \operatorname sin \theta ) ^ 2 = a ^ 2 %2B b ^ 2

Answer»

( a sin - b cos )² + ( a cos + b sin)²

= a² ( sin² + cos²) + b² ( sin² + cos²) - 2ab sin cos + 2 ab sin cos

= a² + b²



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