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The line y=mx+c touches the parabola x2=4ay if
  • a)
    c=-am
  • b)
    c=-am
  • c)
    c=-am2
  • d)
    c=a/m2
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
The line y=mx+c touches the parabola x2=4ay ifa)c=-amb)c=-amc)c=-am2d)...
Y= mx + c; x²= 4ay
Subst y in the equation of parabola
x²= 4a(mx + c) 
x²-4amx-4ac = 0
Since the line touches the parabola at one point The above quadratic will have one root 
b²-4ac = 0
b²= 4ac
16a²m² = 4(1)(-4ac) 
16a²m²= -16ac
c=-am²
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Most Upvoted Answer
The line y=mx+c touches the parabola x2=4ay ifa)c=-amb)c=-amc)c=-am2d)...
Y= mx + c; x²= 4ay
Subst y in the equation of parabola
x²= 4a(mx + c)
x²-4amx-4ac = 0
Since the line touches the parabola at one point The above quadratic will have one root
b²-4ac = 0
b²= 4ac
16a²m² = 4(1)(-4ac)
16a²m²= -16ac
c=-am²
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Community Answer
The line y=mx+c touches the parabola x2=4ay ifa)c=-amb)c=-amc)c=-am2d)...
Understanding the problem:
The given line y = mx + c touches the parabola x^2 = 4ay. We need to determine the relationship between the coefficients m and c.

Key points:
- The equation of the parabola is x^2 = 4ay.
- The equation of the tangent line is y = mx + c.
- The line touches the parabola at a single point.

Strategy:
1. Find the point of tangency between the line and the parabola by solving the system of equations formed by the line and the parabola.
2. Substitute the coordinates of the point of tangency into the equation of the line to determine the relationship between m and c.

Solution:
1. Substituting y = mx + c into the equation of the parabola x^2 = 4ay, we get:
x^2 = 4a(mx + c)
x^2 = 4amx + 4ac
x^2 - 4amx - 4ac = 0
2. Since the line touches the parabola at a single point, the discriminant of this quadratic equation must be zero:
(4am)^2 - 4*(-4a)*(-4ac) = 0
16a^2m^2 - 64ac = 0
16a(m^2 - 4c) = 0
3. For the line to touch the parabola, m^2 - 4c = 0
Therefore, c = m^2/4

Conclusion:
The correct relationship between the coefficients m and c is c = m^2/4, which is given in option C.
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