Math Problem Statement

Determine the equation of the line that passes through the point T(1, -2), and with the positive part of the x axis closes an angle twice as large as the line 9x - 3y + 11 = 0

Solution

To determine the equation of the line that passes through the point T(1,2)T(1, -2) and closes an angle with the positive part of the x-axis that is twice as large as the angle closed by the line 9x3y+11=09x - 3y + 11 = 0, we can follow these steps:

Step 1: Find the slope of the given line.

The equation of the line is given as 9x3y+11=09x - 3y + 11 = 0. To find the slope, we need to express this equation in slope-intercept form, y=mx+cy = mx + c.

9x3y+11=09x - 3y + 11 = 0

3y=9x11-3y = -9x - 11

y=3x+113y = 3x + \frac{11}{3}

Here, the slope m1m_1 of the given line is 3.

Step 2: Determine the angle with the x-axis.

The slope m1m_1 of a line is related to the angle θ1\theta_1 that the line makes with the positive x-axis by the following relation:

tan(θ1)=m1=3\tan(\theta_1) = m_1 = 3

So,

θ1=tan1(3)\theta_1 = \tan^{-1}(3)

Step 3: Find the angle for the new line.

Let the angle that the required line makes with the positive x-axis be θ2\theta_2. According to the problem, θ2=2θ1\theta_2 = 2\theta_1.

Step 4: Find the slope of the new line.

We know that:

tan(θ2)=tan(2θ1)\tan(\theta_2) = \tan(2\theta_1)

Using the double-angle formula for tangent:

tan(2θ1)=2tan(θ1)1tan2(θ1)\tan(2\theta_1) = \frac{2\tan(\theta_1)}{1 - \tan^2(\theta_1)}

Substituting tan(θ1)=3\tan(\theta_1) = 3:

tan(2θ1)=2×3132=619=68=34\tan(2\theta_1) = \frac{2 \times 3}{1 - 3^2} = \frac{6}{1 - 9} = \frac{6}{-8} = -\frac{3}{4}

So, the slope m2m_2 of the required line is 34-\frac{3}{4}.

Step 5: Use the point-slope form to find the equation of the line.

The line passes through the point T(1,2)T(1, -2) and has a slope m2=34m_2 = -\frac{3}{4}. The point-slope form of the equation of a line is given by:

yy1=m(xx1)y - y_1 = m(x - x_1)

Substituting (x1,y1)=(1,2)(x_1, y_1) = (1, -2) and m=34m = -\frac{3}{4}:

y+2=34(x1)y + 2 = -\frac{3}{4}(x - 1)

Multiply both sides by 4 to eliminate the fraction:

4(y+2)=3(x1)4(y + 2) = -3(x - 1)

4y+8=3x+34y + 8 = -3x + 3

3x+4y=53x + 4y = -5

So, the equation of the required line is:

3x+4y+5=0\boxed{3x + 4y + 5 = 0}

Would you like any details or have any questions?

Here are 5 related questions for further exploration:

  1. How can the angle of inclination of a line be derived from its slope?
  2. What is the geometric interpretation of the tangent function in the context of a line’s slope?
  3. How do different transformations affect the slope of a line?
  4. How can the equation of a line be determined if two points on the line are known?
  5. How would the problem change if the angle was three times as large instead of twice?

Tip: When working with slopes, remember that positive slopes indicate lines that rise as they move from left to right, while negative slopes indicate lines that fall.

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Math Problem Analysis

Mathematical Concepts

Geometry
Trigonometry
Lines and Angles

Formulas

Point-slope form of a line equation
Double-angle formula for tangent

Theorems

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Suitable Grade Level

Grades 10-12