Find an equation of the tangent line to the given curve at the specified point.
y = 1/(sinx + cosx) , (0, 1)
and
y = tanx(sinx + cosx) , (π/2, 1)
Where, exactly, is your difficulty? Do you know how to differentiate these functions, using the chain rule, as Sambit suggested, for the first one and the product rule for the second? Do you know how to form the equation of the tangent line after you have the derivative?