Posted by **calculus** on Thursday, September 19, 2013 at 11:49am.

if y=cosx.sinx find dy/dx

- calculus -
**Steve**, Thursday, September 19, 2013 at 11:53am
just use the product rule

If y = fg, then

y' = f'g + fg'

So,

dy.dx = -sinx.sinx + cosx.cosx

= cos^2x - sin^2x

= cos2x

Or, you could have noticed that

y = 1/2 sin2x, so

y' = cos2x

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