Answer
$$3\ln 7$$
Work Step by Step
$$\eqalign{
& \int_1^7 {\frac{3}{x}} dx \cr
& = 3\int_1^7 {\frac{1}{x}} dx \cr
& {\text{integrate using }}\int {\frac{1}{x}} dx = \ln \left| x \right| + C \cr
& = 3\left( {\ln \left| x \right|} \right)_1^7 \cr
& {\text{use the fundamental theorem of calculus }}\int_a^b {f\left( x \right)} dx = F\left( b \right) - F\left( a \right).\,\,\,\,\left( {{\text{see page 281}}} \right) \cr
& = 3\left( {\ln \left| 7 \right| - \ln \left| 1 \right|} \right) \cr
& = 3\ln 7 \cr} $$
