The equation y = -4.2t^2 + 42t + 18.9 describes the height (in meters) of a ball tossed up in the air at 42 meters per second from a height of 18.9 meters from the ground, as a function of time in seconds. In how many seconds will the ball reach maximum height?
+2666 The maximum value is \(18.9 - {1764\over-16.8} = 123.9\). Subsitute the equation like this:\(123.9=-4.2t^2+42t+18.9\). Solve for \(t\), and you get \(\color{brown}\boxed 5\)
+118609 The equation y = -4.2t^2 + 42t + 18.9 describes the height (in meters) of a ball tossed up in the air at 42 meters per second from a height of 18.9 meters from the ground, as a function of time in seconds. In how many seconds will the ball reach maximum height?
This is a concave down parabola, the max will be when t = axis of symmetry
max height will be reached when t = -42/-8.4 = 5seconds
Just as BuilderBoi already said 
+2666 The x-value of the vertex can be also be found by doing \(-b\over2a\), in a quadratic equation with the format \(a^2 + bx + c = 0\).
This also yields \(\color{brown}\boxed5\)
