Question 423339
if i understood your question correctly, you have a formula that is:


4.905*t^2 - 90*t - 150 = 0


you want to find the roots of this equation.


you use the quadratic formula.


this give you an answer of:


x = 19.88641 
or:
x = -1.53779


round these to the nearest 10th and you get:


x = 19.9 
or:
x = -1.5


the 19.9 looks like the number you are showing.


from what i can see, it is one of the roots of the quadratic equation of:


4.905*t^2 - 90*t - 150 = 0


the standard form of a quadratic equation is:


ax^2 + bx + c = 0


this makes:


a = 4.905
b = -90
c = -150


the quadratic formula give you:


{{{x = (-b +- sqrt(b^2-4ac))/(2a)}}}


you solve by plugging in the values for a,b,c derived from above.


the values of x = 19.9 and x = -1.5 are the roots of the quadratic equation.


these are the value of x when the graph of the equation crosses the x-axis.


the graph of your equation of y = 4.905*t^2 - 90*t - 150 looks like this:


{{{graph(600,600,-5,25,-800,800,4.905*x^2 - 90*x - 150)}}}