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<p>&nbsp;</p><p><strong>Pembahasan&nbsp;</strong></p><p><i>Ingat: cos 2x = 1 - 2 sin² x&nbsp;</i> &nbsp; &nbsp; &nbsp;&nbsp;</p><p>&nbsp;</p><p>4 sin² 2x - 2 = -2. (1 - 2 sin² 2x) &nbsp; &nbsp; &nbsp; &nbsp;</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = -2. (cos 4x)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = -2 cos 4x &nbsp; &nbsp; ===&gt;&nbsp;<i> <strong>terbukti</strong></i></p>