\(B=cos\left(270^0-\alpha\right)-2\cdot sin\left(\alpha-450^0\right)+cos\left(\alpha+900^0\right)+2\cdot sin\left(720^0-\alpha\right)+cos\left(540^0-\alpha\right)\)
\(=cos\left(180^0+90^0-a\right)-2\cdot sin\left(a-90^0\right)+cos\left(a+180^0+2\cdot360^0\right)+2\cdot sin\left(-\alpha\right)+cos\left(180^0-\alpha\right)\)
\(=-cos\left(90^0-\alpha\right)+2\cdot sin\left(90^0-\alpha\right)+cos\left(\alpha+180^0\right)-2\cdot sin\alpha-cos\alpha\)
\(=-sin\alpha+2cos\alpha-cos\alpha-2\cdot sin\alpha-cos\alpha\)
\(=-3\cdot sin\alpha\)
Sửa đề: \(A=2\cdot sin\left(90^0+\alpha\right)+cos\left(1260^0-\alpha\right)+tan\left(630^0+\alpha\right)\cdot tan\left(1260^0-\alpha\right)\)
\(=2\cdot cos\alpha+cos\left(180^0-\alpha\right)+tan\left(180^0+\alpha\right)\cdot tan\left(180^0-\alpha\right)\)
\(=2\cdot cos\alpha-cos\alpha+\dfrac{sin\left(180^0+\alpha\right)}{cos\left(180^0+\alpha\right)}\cdot\left(-tan\alpha\right)\)
\(=cos\alpha+\dfrac{cos\alpha}{-sin\alpha}\cdot\dfrac{-sin\alpha}{cos\alpha}=cos\alpha+1\)
