Math Problem Statement

Soit A(-4 ; -1) et B(5 ; 0) deux points dans un repère du plan. Calculer les coordonnées des points M et N tels que : (a) 3\overrightarrow{AM} + 2\overrightarrow{BM} = \overrightarrow{O} (b) -3\overrightarrow{BN} + 2\overrightarrow{AB} = 2\overrightarrow{NA}

Solution

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Problem Overview:

We are given two points in a plane:

  • A(4,1)A(-4, -1)
  • B(5,0)B(5, 0)

We need to find the coordinates of the points MM and NN such that:
(a) 3AM+2BM=03\overrightarrow{AM} + 2\overrightarrow{BM} = \overrightarrow{0}
(b) 3BN+2AB=2NA-3\overrightarrow{BN} + 2\overrightarrow{AB} = 2\overrightarrow{NA}


Step 1: Solve Part (a)

We express AM\overrightarrow{AM} and BM\overrightarrow{BM} in terms of coordinates.

Vectors:

  • AM=(x(4),y(1))=(x+4,y+1)\overrightarrow{AM} = (x - (-4), y - (-1)) = (x + 4, y + 1)
  • BM=(x5,y0)=(x5,y)\overrightarrow{BM} = (x - 5, y - 0) = (x - 5, y)

Substitute these into the equation 3AM+2BM=03\overrightarrow{AM} + 2\overrightarrow{BM} = \overrightarrow{0}:
3(x+4,y+1)+2(x5,y)=(0,0)3(x + 4, y + 1) + 2(x - 5, y) = (0, 0)

Expand the equation:
(3(x+4)+2(x5),3(y+1)+2y)=(0,0)(3(x + 4) + 2(x - 5), 3(y + 1) + 2y) = (0, 0)

Simplify each component:

  1. For the xx-component:
    3(x+4)+2(x5)=3x+12+2x10=5x+2=03(x + 4) + 2(x - 5) = 3x + 12 + 2x - 10 = 5x + 2 = 0
    Solve:
    5x=2    x=255x = -2 \implies x = -\frac{2}{5}

  2. For the yy-component:
    3(y+1)+2y=3y+3+2y=5y+3=03(y + 1) + 2y = 3y + 3 + 2y = 5y + 3 = 0
    Solve:
    5y=3    y=355y = -3 \implies y = -\frac{3}{5}

Thus, the coordinates of MM are:
M(25,35)M\left(-\frac{2}{5}, -\frac{3}{5}\right)


Step 2: Solve Part (b)

Vectors:

  • BN=(x5,y0)=(x5,y)\overrightarrow{BN} = (x - 5, y - 0) = (x - 5, y)
  • AB=(5(4),0(1))=(9,1)\overrightarrow{AB} = (5 - (-4), 0 - (-1)) = (9, 1)
  • NA=((4)x,(1)y)=(4x,1y)\overrightarrow{NA} = ((-4) - x, (-1) - y) = (-4 - x, -1 - y)

Substitute these into the equation 3BN+2AB=2NA-3\overrightarrow{BN} + 2\overrightarrow{AB} = 2\overrightarrow{NA}:
3(x5,y)+2(9,1)=2(4x,1y)-3(x - 5, y) + 2(9, 1) = 2(-4 - x, -1 - y)

Expand each term:

  1. 3BN=(3(x5),3y)=(3x+15,3y)-3\overrightarrow{BN} = (-3(x - 5), -3y) = (-3x + 15, -3y)
  2. 2AB=(29,21)=(18,2)2\overrightarrow{AB} = (2 \cdot 9, 2 \cdot 1) = (18, 2)
  3. 2NA=(2(4x),2(1y))=(82x,22y)2\overrightarrow{NA} = (2(-4 - x), 2(-1 - y)) = (-8 - 2x, -2 - 2y)

Substitute back into the equation:
(3x+15+18,3y+2)=(82x,22y)(-3x + 15 + 18, -3y + 2) = (-8 - 2x, -2 - 2y)

Simplify each component:

  1. For the xx-component:
    3x+33=82x-3x + 33 = -8 - 2x
    Solve:
    33+8=3x2x    x=4133 + 8 = 3x - 2x \implies x = 41

  2. For the yy-component:
    3y+2=22y-3y + 2 = -2 - 2y
    Solve:
    2+2=3y2y    y=42 + 2 = 3y - 2y \implies y = 4

Thus, the coordinates of NN are:
N(41,4)N(41, 4)


Final Answer:

  • M(25,35)M\left(-\frac{2}{5}, -\frac{3}{5}\right)
  • N(41,4)N(41, 4)

Would you like further explanations for any step?

Related Questions:

  1. How do we interpret vectors in coordinate geometry problems like this?
  2. Why do we need to balance both the xx- and yy-components in vector equations?
  3. Can we solve this problem using a different approach, such as matrices?
  4. What are the geometrical meanings of MM and NN here?
  5. How can we verify the solutions for MM and NN are correct?

Tip:

Always carefully define the components of vectors when solving equations, as clarity helps avoid errors in sign or calculation.

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Math Problem Analysis

Mathematical Concepts

Vectors
Coordinate Geometry
Linear Equations

Formulas

Vector addition and scalar multiplication
Component form of a vector
Balancing equations for vector components

Theorems

Linear combinations of vectors

Suitable Grade Level

Grades 10-12