-9.8t^2-15t+100=100

Solution for -9.8t^2-15t+100=100 equation:

-9.8t^2-15t+100=100

We move all terms to the left:

-9.8t^2-15t+100-(100)=0

We add all the numbers together, and all the variables

-9.8t^2-15t=0

a = -9.8; b = -15; c = 0;
Δ = b2-4ac
Δ = -152-4·(-9.8)·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-15}{2*-9.8}=\frac{0}{-19.6}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+15}{2*-9.8}=\frac{30}{-19.6}
=-1+7.4285714285714/14
$