First slide
Parabola
Question

The equation of the line touching both the parabola y2 = 4x and x2=32y is ax+by+c=0. Then the value of a + b +c is

Easy
Solution

The equation of tangent in terms of the slope of the parabola y2 = 4x is y=mx+1m
Since (i) is also the tangent of x2 = - 32 !, wa have
x2=32mx+1mor  x2+32mx+32m=0
The above equation must have equal roots.
Hence, its discriminant must be zero. Therefore,

(32m)2=4×1×32mi.e.,m3=18 or m=12

From (i), y=x2+2  or  x2y+4=0

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