# Maths Homework.

• Mar 20th 2012, 02:42 AM
HollieMay2600
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?
• Mar 20th 2012, 02:49 AM
Prove It
Re: Maths Homework.
What is m?
• Mar 20th 2012, 03:02 AM
HollieMay2600
Re: Maths Homework.
Quote:

Originally Posted by Prove It
What is m?

m is metres
• Mar 20th 2012, 03:31 AM
princeps
Re: Maths Homework.
Quote:

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 :

$40t=25 \Rightarrow t=\frac{5}{8}$
• Mar 20th 2012, 05:49 AM
HallsofIvy
Re: Maths Homework.
Quote:

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
$\frac{40\pm\sqrt{1600+ 1300}}{26}= \frac{40\pm\sqrt{2900}}{26}$.

Quote:

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

hence :

$40t=25 \Rightarrow t=\frac{5}{8}$
• Mar 20th 2012, 05:56 AM
princeps
Re: Maths Homework.
Yes it is clear now , after original post is edited .