I have been asked to calculate the maximum height a ball can achieve after being lauched, using;

h = - 4.9t^2 + 19.6t - 12.6

I knew straight away I required the time, so I did the following;

t = -b + or - square root b^2 - 4ac / 2a

t =- 19.6 + or - square root 19.6^2 - 4 (- 4.9)(- 12.6)

2 x ( - 4.9)

t =- 19.6 + or - square root 384.16 - 246.96

2 x ( - 4.9)

t =- 19.6 + or - square root 137.20

2 x( - 9.80)

t =- 19.6 + or - 11.71

- 9.80

t =- 7.89

- 9.80

t1 = 0.81

t2 =- 19.6 + or - 11.71

- 9.80

t2 =- 31.31

- 9.80

t2 = 3.20

I then used both routes to conclude the height in metres to determine if there was any significant difference, there wasn't so I will use t2;

h = - 4.9 x 3.20^2 + 19.6 x 3.20 - 12.6

h = - 50.18 + 62.72 - 12.6

h = 0

This is the third answer I have had using the above formula?

I have had first 65m, then 34m and now 0 metres?

I can see I must have tapped a interger in wrong in the calculator or not used it correctly, but can I ask, does the above now look like I have got it right?

Thanks

David