Math Problem Statement

Soient f et g les deux fonctions définies sur ℝ par f(x) = 2x - 3 et g(x) = (2 - 3x)/4. Tracer les courbes représentatives de f et g dans un repère orthonormé d’échelle 2cm pour une unité. Déterminer par le calcul les coordonnées des éventuels points d’intersection des deux courbes.

Solution

The exercise provides two functions f(x)=2x3f(x) = 2x - 3 and g(x)=23x4g(x) = \frac{2 - 3x}{4} and requires the following tasks:

1. Graph the curves of ff and gg on an orthonormal coordinate system with a scale of 2 cm per unit.

Before plotting, let’s analyze each function.

  • For f(x)=2x3f(x) = 2x - 3:

    • The slope is 2, meaning the line is increasing.
    • The y-intercept is -3, so the line passes through (0,3)(0, -3).
  • For g(x)=23x4g(x) = \frac{2 - 3x}{4}:

    • Simplifying this expression: g(x)=243x4=123x4g(x) = \frac{2}{4} - \frac{3x}{4} = \frac{1}{2} - \frac{3x}{4}.
    • This is a linear function with slope 34-\frac{3}{4} and y-intercept 12\frac{1}{2}, meaning the line is decreasing and passes through (0,0.5)(0, 0.5).

2. Determine by calculation the coordinates of the intersection points of the two curves.

To find the points of intersection, we need to solve the equation where f(x)=g(x)f(x) = g(x).

So, set: 2x3=123x42x - 3 = \frac{1}{2} - \frac{3x}{4}

Let's solve this equation step by step:

2x3=123x42x - 3 = \frac{1}{2} - \frac{3x}{4} Multiply the whole equation by 4 to eliminate the fractions:

4(2x3)=4(123x4)4(2x - 3) = 4\left(\frac{1}{2} - \frac{3x}{4}\right)

This simplifies to:

8x12=23x8x - 12 = 2 - 3x

Now, add 3x3x to both sides to combine the terms with xx:

8x+3x12=28x + 3x - 12 = 2

Simplify:

11x12=211x - 12 = 2

Now, add 12 to both sides:

11x=1411x = 14

Finally, divide by 11:

x=1411x = \frac{14}{11}

Substitute this value of xx into either f(x)f(x) or g(x)g(x) to find yy.

Substitute into f(x)=2x3f(x) = 2x - 3:

f(1411)=2×14113=28113=28113311=511f\left(\frac{14}{11}\right) = 2 \times \frac{14}{11} - 3 = \frac{28}{11} - 3 = \frac{28}{11} - \frac{33}{11} = \frac{-5}{11}

So, the point of intersection is (1411,511)\left( \frac{14}{11}, \frac{-5}{11} \right).


Would you like further clarification on the graphing part or any other aspect of this problem?

Relative Questions:

  1. How do you find the slope of a line from its equation?
  2. How do the slopes of two lines affect their points of intersection?
  3. What does the y-intercept of a linear function represent?
  4. What is the graphical meaning of solving f(x)=g(x)f(x) = g(x)?
  5. How can you interpret the result of x=1411x = \frac{14}{11} geometrically?

Tip:

When solving equations involving fractions, multiplying through by the least common denominator helps eliminate the fractions quickly.

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Math Problem Analysis

Mathematical Concepts

Linear Functions
Graphing
Algebra

Formulas

f(x) = 2x - 3
g(x) = (2 - 3x)/4
Equation of a line: y = mx + b
Solving equations: 2x - 3 = (2 - 3x)/4

Theorems

Intersection of two lines occurs when f(x) = g(x)

Suitable Grade Level

Grades 9-11