A simple confusion: Showing projectile is launched horizontally

AI Thread Summary
The discussion focuses on proving that a ball is projected horizontally based on its trajectory equation, y = -0.05x^2. The mark scheme indicates that since x tan a = 0, the angle a must be 0, confirming a horizontal launch. A participant expresses confusion about the origin of the x in the equation. Another contributor clarifies that tan a represents the derivative of the function at x=0, which is zero, thus supporting the horizontal projection conclusion. The conversation emphasizes understanding the relationship between the trajectory's derivative and the launch angle.
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The equation of trajectory of ball B is y = -0.05x^2 where y is vertical displacement and x is horizontal. Prove that the ball is projected horizontallyFor this, the mark scheme says
x tan a = 0 so a =0
Since the angle between ball and surface is 0 the object is projected horizontally.
I can't work out how is x tan a = 0
 
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The problem statement got lost somehow.
 
Please check again
 
I don't see where the x would come from.

tan a is the derivative of your function at x=0. The derivative is 0, therefore tan a = 0.
 
How do you know the derivative is 0?
 
Got it thanks
 

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