SOLUTION: -90(t) + 4.905 (t*t) -150 = 19.9! !! can u explain to me how they found t=19.9 ?

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Question 423339: -90(t) + 4.905 (t*t) -150 = 19.9! !! can u explain to me how they found t=19.9 ?
Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
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+=+%28-b+%2B-+sqrt%28b%5E2-4ac%29%29%2F%282a%29

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%28600%2C600%2C-5%2C25%2C-800%2C800%2C4.905%2Ax%5E2+-+90%2Ax+-+150%29