If the differential equation of all the straight lines which are at a ...
The given family of lines can be represented by the equation,
xcosα + ysin α = 10 ...(1)
where α is an arbitrary constant.
Differentiating we have,
cosα + sinαy
1 = 0 ...(2)
Multiplying (2) by x and subtracting it from (1),
⇒ (y − xy
1)sinα = 10 ...(3)
Multiplying (1) by y
1 and (2) by y and subtracting,
xy
1cosα − ycosα = 10y
1⇒ (xy
1 − y)cosα = 10y
1...(4)
Squaring and adding (3) and (4) we get, (y − xy
1)
2 = 100(1 + y
12)
Now on comparing, we get A = 100.
If the differential equation of all the straight lines which are at a ...
Given differential equation:
The given differential equation is (y - xy')^2 = A(1 + y'^2), where y' represents dy/dx.
Finding the value of A:
To find the value of A, we need to compare the given differential equation with the general equation of straight lines at a fixed distance from the origin.
The general equation of straight lines at a fixed distance 'd' from the origin is of the form: xcosθ + ysinθ = ±d.
Comparing the given differential equation with the general equation, we get:
- Comparing y - xy' with y, we get cosθ = 1.
- Comparing -xy' with sinθ, we get sinθ = -1.
- Therefore, cosθ = 1 and sinθ = -1, which implies θ = 180 degrees.
- Substituting θ = 180 degrees into the general equation, we get xcos180 + ysin180 = ±10.
- This simplifies to -x + y = ±10, which can be written as y = x ± 10.
Comparing this with the given differential equation, we get:
(y - xy')^2 = A(1 + y'^2) becomes (x ± 10)^2 = A(1 + 1) => x^2 ± 20x + 100 = 2A.
By comparing the coefficients, we find that A = 100.
Therefore, the value of A is 100.