Exercise $2\mathrm{.}5$

Find the difference quotient $\frac{f(x)-f(a)}{x-a}$ for the following functions:

a$)f(x)=3x$

b$)f(x)=4x-7$

c$)f(x)=x^2-3x$

d$)f(x)=x^{2}4x-5$

e$)f(x)=7x^{2}2x$

f$)f(x)=\frac{1}{x}$