1.

If the line lx + my + n = 0 touches the parabola y2 = 4ax, then(a)   In = am(b)  In2 = am2(c)  l2n = am2(d)   In = am2

Answer»

Correct option  (D) ln = am2 

Explanation :

Suppose lx + my + n = 0 touches the parabola y2 = 4ax at (at2, 2at). However, ty = x + at2 is the equation of the tangent at (at2, 2at). Therefore

l/1 = m/-t = n/at2

⇒ - m/l = t = -n/ma

⇒ am2 = ln



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