jawab soal 2

$\Leftrightarrow 2\: cos(2x-15)\: =-\sqrt{2},\: 0\leq x\leq 180$

$\Leftrightarrow cos(2x-15)\: =-\frac{1}{2}\sqrt{2}$

$\Leftrightarrow cos(2x-15)\: =cos135$

$\Leftrightarrow 2x-15\: =135+n360\textrm{ atau }2x-15\: =-135+n360$

$*\Leftrightarrow 2x-15\: =135+n360$

   $\Leftrightarrow 2x\: =150+n360$

   $\Leftrightarrow x\: =75+n180$

   $\Leftrightarrow x\: =75$

$*\Leftrightarrow 2x-15\: =-135+n360$

   $\Leftrightarrow 2x\: =-120+n360$

   $\Leftrightarrow x\: =-60+n180$

   $\Leftrightarrow x\: =120$

Hp = {75, 120}

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jawab soal 2