Derivative of Cosine: Solutions

$d dt 4 cos (t)
&sp;=&sp; -4 sin (x)$
$d dr (r^2^cos (r)) &sp;=&sp; 2r - r^2^(- sin (r) ) cos^2^(r) &sp;=&sp; 2r+r^2^sin (r) cos^2^(r)$
$D_x_sin (2x) &sp;=&sp;
D_x_2 sin (x) cos (x) &sp;=&sp;
2 cos^2^(x) - 2 sin^2^(x) &sp;=&sp;
2 cos (2x)$

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