Given,
The x-intercept of a focal chord of the parabola y2=8x+4y+4 is 3,
Now simplifying equation of the given parabola we get,
y2=8x+4y+4
⇒(y−2)2=8(x+1)
Now on comparing with standard parabola y2=4ax we get,
a=2,X=x+1,Y=y−2
Hence, the vertex is (−1,2) and focus is (1,2)
So, equation of line passing through focus is given by y−2=m(x−1)
Now, putting (3,0) {as given x−intercept of focal chord is 3} in the above line we get, m=−1
So, equation of chord will be y=3−x,
Now putting the value of y=3−x in parabola (y−2)2=8(x+1) we get,
⇒(1−x)2=8(x+1)
⇒x2−10x−7=0
⇒∣x1−x2∣=102+4×7=128
⇒∣y1−y2∣=∣3−x1−(3−x2)∣=∣x2−x1∣=128
Length of focal chord ∣x2−x1∣2+∣y2−y1∣2=256=16.