You're a US general serving in Iraq and have been given orders to bomb a target 20km away.
The missile launcher has been programed with an equation
showing the parabolic trajectory of the missile.
If the equation is given in the general form ,
how can you know if it will hit the target?
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We know two points on the parabola: . and .
Plug them into the general equation: .
. . The equation (so far) is: .
. . The equation is: .
Note: Since we want a down-opening parabola, .
If the general doesn't care how high the missile goes,
. . can be any negative quantity.