1.

For which value of m is the line y = mx + 1 a tangent to the curve y2 = 4x ?(a) 1/2(b) 1(c) 2(d) 3

Answer»

Option : (b)

y = mx + 1 … . . (1) and 

y2 = 4x … … (2) 

Substituting (1) in (2) : 

(mx + 1)2 = 4x 

⇒ m2x2 + (2m − 4)x + 1 = 0 … … . . (3) 

As line is tangent to the curve 

⇒ line touches the curve at only one point 

⇒ (2m − 4)2 − 4m2 = 0 

⇒ m = 1



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