Đáp án:
$H=-cos2\alpha-tan^4\alpha\\
A=0$
Giải thích các bước giải:
$H=sin^2(180^{\circ}-\alpha)+tan^2(180^{\circ}-\alpha).tan^2(\alpha+270^{\circ})+sin(90^{\circ}+\alpha)cos(360^{\circ}-\alpha)\\
=sin^2\alpha-tan^2\alpha.tan^2(\alpha+180^{\circ}+90^{\circ})-cos\alpha.cos(180^{\circ}+180^{\circ}-\alpha)\\
=sin^2\alpha-tan^2\alpha.tan^2(\alpha+90^{\circ})+cos\alpha.cos(180^{\circ}-\alpha)\\
=sin^2\alpha-tan^2\alpha.tan^2\alpha-cos\alpha.cos\alpha\\
=sin^2\alpha-tan^2\alpha.tan^2\alpha-cos^2\alpha\\
=-cos2\alpha-tan^4\alpha\\
A=cos\left ( \alpha-\frac{\pi}{2} \right )+sin\left ( \frac{\pi}{2}-\alpha \right )-cos\left ( \frac{\pi}{2}+\alpha \right )-sin\left ( \frac{\pi}{2}+\alpha \right )\\
=-sin\alpha+cos\alpha +sin\alpha -cos\alpha\\
=0$
