25=25-5t-5t^2

Solution for 25=25-5t-5t^2 equation:

25=25-5t-5t^2

We move all terms to the left:

25-(25-5t-5t^2)=0

We get rid of parentheses

5t^2+5t-25+25=0

We add all the numbers together, and all the variables

5t^2+5t=0

a = 5; b = 5; c = 0;
Δ = b2-4ac
Δ = 52-4·5·0
Δ = 25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25}=5$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(5)-5}{2*5}=\frac{-10}{10}
=-1
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(5)+5}{2*5}=\frac{0}{10}
=0
$