b2-10b-21=3

Solution for b2-10b-21=3 equation:

b2-10b-21=3

We move all terms to the left:

b2-10b-21-(3)=0

We add all the numbers together, and all the variables

b^2-10b-24=0

a = 1; b = -10; c = -24;
Δ = b2-4ac
Δ = -102-4·1·(-24)
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-14}{2*1}=\frac{-4}{2}
=-2
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+14}{2*1}=\frac{24}{2}
=12
$