Math Problem Statement

x/3 - y/4 = 1 y² -2y = 4x + 5

find x and y

Solution

We are solving the system of equations:

  1. x3y4=1\frac{x}{3} - \frac{y}{4} = 1
  2. y22y=4x+5y^2 - 2y = 4x + 5

Step 1: Simplify the equations

  1. Multiply through by the common denominator of 12 in the first equation: 4x - 3y = 12 \tag{1'}

  2. Rewrite the second equation: y^2 - 2y - 4x - 5 = 0 \tag{2'}

Now the system becomes: 4x - 3y = 12 \tag{1'} y^2 - 2y - 4x - 5 = 0 \tag{2'}

Step 2: Express xx in terms of yy from (1')

From (1)(1'): 4x = 3y + 12 \implies x = \frac{3y + 12}{4} \tag{3}

Step 3: Substitute xx into (2')

Substitute x=3y+124x = \frac{3y + 12}{4} into (2)(2'): y22y4(3y+124)5=0y^2 - 2y - 4\left(\frac{3y + 12}{4}\right) - 5 = 0 Simplify: y22y(3y+12)5=0y^2 - 2y - (3y + 12) - 5 = 0 y22y3y125=0y^2 - 2y - 3y - 12 - 5 = 0 y^2 - 5y - 17 = 0 \tag{4}

Step 4: Solve the quadratic equation for yy

The quadratic equation is: y25y17=0y^2 - 5y - 17 = 0 Solve using the quadratic formula: y=b±b24ac2a,a=1,b=5,c=17y = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}, \quad a = 1, \, b = -5, \, c = -17 y=(5)±(5)24(1)(17)2(1)y = \frac{-(-5) \pm \sqrt{(-5)^2 - 4(1)(-17)}}{2(1)} y=5±25+682y = \frac{5 \pm \sqrt{25 + 68}}{2} y=5±932y = \frac{5 \pm \sqrt{93}}{2} y=5±932y = \frac{5 \pm \sqrt{93}}{2}

Thus: y1=5+932,y2=5932y_1 = \frac{5 + \sqrt{93}}{2}, \quad y_2 = \frac{5 - \sqrt{93}}{2}

Step 5: Find corresponding xx values

Using x=3y+124x = \frac{3y + 12}{4}, substitute each yy value:

For y1=5+932y_1 = \frac{5 + \sqrt{93}}{2}: x1=3(5+932)+124x_1 = \frac{3\left(\frac{5 + \sqrt{93}}{2}\right) + 12}{4} x1=15+3932+124x_1 = \frac{\frac{15 + 3\sqrt{93}}{2} + 12}{4} x1=15+393+2424x_1 = \frac{\frac{15 + 3\sqrt{93} + 24}{2}}{4} x1=39+3938x_1 = \frac{39 + 3\sqrt{93}}{8}

For y2=5932y_2 = \frac{5 - \sqrt{93}}{2}: x2=3(5932)+124x_2 = \frac{3\left(\frac{5 - \sqrt{93}}{2}\right) + 12}{4} x2=153932+124x_2 = \frac{\frac{15 - 3\sqrt{93}}{2} + 12}{4} x2=15393+2424x_2 = \frac{\frac{15 - 3\sqrt{93} + 24}{2}}{4} x2=393938x_2 = \frac{39 - 3\sqrt{93}}{8}

Final Solution:

The solutions are: (x1,y1)=(39+3938,5+932)(x_1, y_1) = \left(\frac{39 + 3\sqrt{93}}{8}, \frac{5 + \sqrt{93}}{2}\right) (x2,y2)=(393938,5932)(x_2, y_2) = \left(\frac{39 - 3\sqrt{93}}{8}, \frac{5 - \sqrt{93}}{2}\right)

Let me know if you need detailed numeric approximations or further clarifications!


Here are five related questions:

  1. How is the quadratic formula derived?
  2. What are other methods to solve simultaneous equations?
  3. Can this problem be solved graphically?
  4. How does the discriminant of a quadratic equation affect the solution?
  5. How can we interpret these solutions geometrically?

Tip: Always verify solutions by substituting them back into the original equations!

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Math Problem Analysis

Mathematical Concepts

Algebra
Simultaneous Equations
Quadratic Equations

Formulas

Linear equation formula ax + by = c
Quadratic equation formula: ax^2 + bx + c = 0
Quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a

Theorems

Quadratic formula theorem
System of equations elimination and substitution methods

Suitable Grade Level

Grades 9-12