### Home > PC > Chapter 9 > Lesson 9.2.2 > Problem9-82

9-82.

Use your slopes from problem 9-81 to write the equation of the line which is tangent to each of the functions at the point when $x = 2$. Use point-slope form.

1. $f ( x ) = 2 x ^ { 2 }$

From 9-81, $m = 8$$f\left(2\right) = \left(2\right)2^2 = 8$
Equation of line: $y − 8 = 8\left(x − 2\right)$

1. $f ( x ) = 3 ^ { x }$

From 9-81, $m = 9.888$, $y − 9 = 9.888\left(x − 2\right)$
Equation of line: $y = 9.888\left(x − 2\right) + 9$

1. $f ( x ) = \log x$

From 9-81, $m = 0.217$, $f\left(2\right) = \log \left(2\right) = 0.301$
Equation of line: $y − 0.301 = 0.217\left(x - 2\right)$
$y = 0.217\left(x − 2\right) + 0.301$

1. $f ( x ) = \ \cos x ( x \text { in radians } )$

From 9-81, $m = −0.909$
$f\left(2\right) = \cos\left(2\right) = −0.416$
Equation of line: $y − \left(−0.416\right) = −0.909\left(x − 2\right)$
$y = −0.909\left(x − 2\right) − 0.416$