1.

Find the co-ordinates of the focus, vertex, equation of the directrix, axis and the length of latus rectum of the parabola (a) y2 = 20x, (b) x2 = 8y, (c) x2 = -16y

Answer»

(a) y2 = 20x 

y2 = 4(5)x

∴ a = 5

Vertex(0,0)(0,0)
Focus(a,0)(5,0)
Axisx-axisy = 0
Directrixx + a = 0x + 5 = 0
Length of latus rectum4a20

(b) x2 = 8y = 4(2)y 

∴ a = 2

Vertex(0,0)(0,0)
Focus(0,a)(0,2)
Axisy-axisx = 0
Directrixy + a = 0y + 2 = 0
Length of latus rectum4a8

(c) x2 = -16y = -4(4)y 

∴ a = 4

Vertex(0,0)(0,0)
Focus(0,-a)(0,-4)
Axisy-axisx = 0
Directrixy - a = 0y - 4 = 0
Length of latus rectum4a16


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