Finding gradient of slope involving angle

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Homework Help Overview

The original poster attempts to find the equations of two straight lines that are inclined at an angle of 45° to the line represented by the equation 2x + y - 3 = 0, while passing through the point (-1, 4). The problem involves understanding the relationship between the slopes of the lines and the angle between them.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the use of the formula tan θ = (m1 - m2)/(1 + m1m2) to relate the slopes of the lines. There are questions about how to assign m1 and m2, and whether the order affects the outcome. Some participants explore the implications of having positive and negative slopes in relation to the angle.

Discussion Status

Participants are actively engaging with the problem, questioning the assignment of slopes and discussing the implications of swapping m1 and m2. There is a recognition that both positive and negative angles are relevant to the problem, indicating a productive exploration of the topic.

Contextual Notes

The discussion includes considerations about the nature of angles formed by slopes and the specific conditions of the problem, such as the requirement for the lines to be at a 45° angle to a given line.

Kurokari
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Homework Statement



Find the equations of both the straight lines that are inclined at an angle of 45 ° with straight line 2x + y - 3 = 0 and passing through the point (-1 , 4)

Homework Equations



tan θ = (m1 - m2)/(1+ m1m2)

The Attempt at a Solution



If I were to use the equation above, how would I know which is m1 and m2? Is there anyway to test it out or deduce which is m1 and which is m2?
 
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Swapping m1 and m2 in the formula is equivalent to negating theta. You are looking for lines that make angle theta to a given line, so that would be both plus and minus. Therefore it does not matter which way you assign m1 and m2.
 
Well what about if there is a negative and and a positive?

Say m1 = -1 and m2 = 2

If we followed the formula, I would get a tanθ,
However if I were to swap them, I would instead get a negative tanθ. Or does this matter?
 
Kurokari said:
Well what about if there is a negative and and a positive?

Say m1 = -1 and m2 = 2

If we followed the formula, I would get a tanθ,
However if I were to swap them, I would instead get a negative tanθ. Or does this matter?
That just says the angle between the m1 and m2 lines is θ. Whether you consider that as plus or minus depends on which of the two lines you start from. In the present problem you are asked for two lines at angle 45 degrees to a given line, so you want both cases.
 

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