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**1. The problem statement, all variables and given/known data**

Calculate the limit as x-->pi/4 of [tan(x-pi/4)+1]/x-pi/4

**2. Relevant equations**

lim h-->0 of [f(x+h)-f(x)]/h = f'(x)

lim x--->a [f(x)-f(a)]/(x-a) = f'(x)

**3. The attempt at a solution**

I've attempted to turn this equation into the form f(x)-f(a)/x-a by letting f(x)=tanx and a=pi/4

This turns into -[-tan(x+a)-tan(a)]/x-a......which isnt the correct derivative form. .I've tried other methods which also turn into similar garble (a minus sign backwards, x-h rather than x+h and the like).

Can anyone see what the problem is? Thanks