Question

The graphs of the function f (given in blue) and g (given in red) are plotted above. Suppose that u(x)=f(x)g(x) and v(x)=f(x)/g(x). Find each of the following:
u'(1) =
v'(1) =

Answer 1

U(x) = f(x).(gx)
v(x) = f(x) /  g(x)

Use chain rule to find u(x) and v(x).

u '(x) = f '(x) g(x) + f(x) g'(x)

v ' (x) = [f '(x) g(x) - f(x) g(x)] / [g(x)]^2

The functions given are piecewise.

You need to use the pieces that include the point x = 1.

You can calculate f '(x) and g '(x) at x =1, as the slopes of the lines that define each function.

And the slopes can be calculated graphycally as run / rise of each graph, around the given point.

f '(x) = slope of f (x); at x = 1, f '(1) = run / rise = 1/1 = 1

g '(x) = slope of g(x); at x = 1, g '(1) = run / rise = 1.5/ 1 = 1.5

You also need f (1) = 1 and g(1) = 2

Then:

u '(1) =  f '(1) g(1) + f(1) g'(1) = 1*2 + 1*1.5 = 2 + 1.5 = 3.5

v ' (x) = [f '(1) g(1) - f(1) g(1)] / [g(1)]^2 = [1*2 -  1*1.5] / (2)^2 = [2-1.5]/4 =

= 0.5/4 = 0.125

Answers:
u '(1) = 3.5
v '(1) = 0.125