a)
y=x*sinx
y'=(x*sinx)' = (x)' * sinx + x * (sinx)' = 1 * sinx + x * cosx = sinx + x*cosx
b)
y=x/(1+x)
y'=(x/(1+x))' =( x' * (1+x) - x * (1+x)' )/(1+x)^2 = ( 1 * (1+x) - x * 1 )/(1+x)^2 =
= ( 1+x - x )/(1+x)^2 = 1/(1+x)^2 = (1+x)^(-2)
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