identitas trigonometri

<p><strong>Pembahasan&nbsp;</strong></p><p>cos²x(1 - tan²x) = cos²x - cos²x. (sin²x/cos²x)&nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= cos²x - sin²x</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= (1 - sin²x) - sin²x</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 1 - 2 sin²x &nbsp; &nbsp; &nbsp;——&gt; <i><strong>terbukti</strong></i></p>