Find the equation of the lines through the point (3, 2) which make an angle of 45° with the line x – 2y = 3.
Let the slope of the required line be m1.
The given line can be written as y = 1/2x - 3/2, which is of the form y = mx + c.
∴ Slope of the given line = m2 = 1/2
It is given that the angle between the required line and line x - 2y - 3 = is 45°.
We know that if θ is the acute angle between line l1 and l2 with slopes m1 and m2 respectively, then
tanθ = |m1 - m2/1 + m1m2|
∴ tan45° = |m1 - m2/1 + m1m2|
1 = |1/2 - m1/1 + m1/2| = |1 - 2m1/2 + m1|
1 = |1 - 2m1/2 + m1| ⇒ 1 = ±1 - 2m1/2 + m1
1 = 1 - 2m1/2 + m1 or 1 = -1 - 2m1/2 + m1
2 + m1 = 1 - 2m1 or 2 + m1 = -1 + 2m1
⇒ m1 = -1/3 or m1 = 3
Case I: m1 = 3
The equation of the line passing through (3, 2) and having a slope of 3 is:
y - 2 = 3(x - 3)
y - 2 = 3x - 9
3x - y = 7
Case II: m1 = -1/3
The equation of the line passing through (3, 2) and having a slope of -1/3 is:
y - 2 = -1/3 (x - 3)
3y - 6 = -x + 3
x + 3y = 9
Therefore, the equations of the lines are 3x - y = 7 and x + 3y = 9.