Finding the global minimum of f(x) from its derivative
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207. After the graphs of the functions $f(x)$ and $f'(x)$ were drawn in a computer program and the coordinate axes were hidden, the following image was obtained when placed in the plane consisting of equal squares.
[Image showing a parabola f(x) and a linear function f'(x) on a grid]
Accordingly, what is the smallest possible value that $f(x)$ can take?
A) $\frac{2}{3}$
B) $\frac{3}{4}$
C) $\frac{5}{3}$
D) $\frac{6}{5}$
E) $\frac{8}{9}$
This question includes visual content: A screenshot of a software interface showing two functions plotted on a grid of equal squares. One curve is a parabola labeled 'f(x)' and the other is a straight line labeled 'f'(x)'. The line has a positive slope and points plotted at equal intervals. The parabola has a vertex point marked. The coordinate axes are hidden.
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Step by Step Written Solution
Hi Tirth, let's solve this problem together. We are looking for the minimum value of the function f(x), which corresponds to the y-coordinate of the parabola's vertex.
Analyzing the Graphs
Let's first establish a coordinate system. Based on the grid, we can identify the vertex of the parabola f(x) and use it as our reference point (x_v, y_v).
The derivative f'(x) is a linear function. By observing the dots on the line, we can determine its slope. It rises two units for every three units it moves to the right, so the slope a is two-thirds.
Integrating the derivative, we get the expression for f(x). Since f'(x) = 2/3(x - x_v), the function is f(x) = 1/3(x - x_v)^2 + y_v.
Now, we identify the intersection point of f(x) and f'(x) from the grid. Looking at the graph, this intersection occurs at a point where x - x_v equals 3.
At this intersection point, the y-values are equal. Let's substitute x - x_v = 3 into both equations.
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