1. ## Maths Homework.

The height s metres of a mass thrown vertically upward at a time t seconds given by

S=40t-13t2

Show when 25m= 40t - 13t2, 13t2 - 40t + 25 = 0

There is something about what you do to one side you have to do to the other?

What is m?

3. ## Re: Maths Homework.

Originally Posted by Prove It
What is m?
m is metres

4. ## Re: Maths Homework.

Originally Posted by HollieMay2600
Show when 25m= 40t - 13t2, - 13t2 - 40t + 25 = 0

There is something about what you do to one side you have to do to the other?
I suppose that this represents system of two equations :

(1) : $-13t_2+40t-25=0$

(2) : $-13t_2-40t+25=0$

(1)+(2) : $-26t_2=0 \Rightarrow t_2=0$

hence :

$40t=25 \Rightarrow t=\frac{5}{8}$

5. ## Re: Maths Homework.

Originally Posted by princeps
I suppose that this represents system of two equations :

(1) : $-13t_2+40t-25=0$

(2) : $-13t_2-40t+25=0$
No. This should be $13t^2- 40t+ 25= 0$ which has, by the quadratic formula, solutions
$\frac{40\pm\sqrt{1600+ 1300}}{26}= \frac{40\pm\sqrt{2900}}{26}$.

(1)+(2) : $-26t_2=0 \Rightarrow t_2=0$

hence :

$40t=25 \Rightarrow t=\frac{5}{8}$

6. ## Re: Maths Homework.

Yes it is clear now , after original post is edited .