The equation of the parabola is of the form x2=−4ay
It passes through (6,−4)
∴ 36=16a⇒ a=94
The equation is x2=−9y .....(1)
To find the solpe at (−6,−4)
Differentiating (1) w.r.t x, we get
2x=−9dydx⇒dydx=−29x
at (−6,−4), dydx=−29×(−6)=43
(i.e.,) tanθ=43;θ=tan−143
∴ the angle of projection is tan−143.