Question
${10^{ - x\,\tan x}}\left[ {\frac{d}{{dx}}({{10}^{x\tan x}})} \right] = $
$= {10^{ - x\tan x}}{.10^{x\tan x}}.\log 10(\tan x + x{\sec ^2}x)$
$= \log 10(\tan x + x{\sec ^2}x)$.
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