Question

Let f(x) = x^2 + 6x.
(A) Find the slope of the secant line joining (3,f(3)) and (9,f(9)).
(B) Find the slope of the secant line joining (5,f(5)) and (5+h,f(5+h)).

Answer 1

Answer:

(A) The slope of secant line is 18.

(B) The slope of secant line is h+16.

Step-by-step explanation:

(A)

The given function is

$f(x)=x^2+6x$

At x=3,

$f(3)=(3)^2+6(3)=27$

At x=9,

$f(9)=(9)^2+6(9)=135$

The secant line joining (3,27) and (9,135). So, the slope of secant line is

$m=\dfrac{y_2-y_1}{x_2-x_1}$

$m=\dfrac{135-27}{9-3}=18$

The slope of secant line is 18.

(B)

The given function is

$f(x)=x^2+6x$

At x=5,

$f(5)=(5)^2+6(5)=55$

At x=5+h,

$f(5+h)=(5+h)^2+6(5+h)=h^2 + 16 h + 55$

The secant line joining (5,55) and $(5+h,h^2 + 16 h + 55)$. So, the slope of secant line is

$m=\dfrac{h^2 + 16 h + 55-55}{5+h-5}$

$m=\dfrac{h^2 + 16 h }{h}$

$m=h+16$

The slope of secant line is h+16.