# Thread: Equation - Changing the subject

1. ## Equation - Changing the subject

Hi,

I'm working through a game graphics book (and I've been learning the math from scratch) and every now and again the author shoves in a bunch of equations and simplifies them, or changes their subject without any explanation of the steps he used (nor has he explained properly in previous chapters).

If anyone could help me figure out how he managed to get the variable t on its own in steps 2 and 3 below I would be grateful.

1.) -1.5 = 5t - 5 t^2
2.) t^2 - t - 0.3 = 0
3.) t = (1 sqrt(1 + 1.2)) / 2

Cheers

GamerMath

2. $\displaystyle -1.5=5t-5t^2$
$\displaystyle 5t^2-5t-1.5=0$
$\displaystyle 5(t^2-t-0.3)=0$
$\displaystyle t^2-t-0.3=0$ -----------2.)

now use the standard equation for the solution for a quadric equation, then you'll get
$\displaystyle t=\frac{1 \pm \sqrt{1+4\times 0.3}}{2}$

i guess t is representing time, so you can eliminate the minus solution which will give the third equation

3. You either need to complete the square or use the quadratic formula.