(1/5)b+(2/5)b=15

Solution for (1/5)b+(2/5)b=15 equation:

(1/5)b+(2/5)b=15

We move all terms to the left:

(1/5)b+(2/5)b-(15)=0


Domain of the equation: 5)b!=0

b!=0/1

b!=0

b∈R


We add all the numbers together, and all the variables

(+1/5)b+(+2/5)b-15=0

We multiply parentheses

b^2+2b^2-15=0

We add all the numbers together, and all the variables

3b^2-15=0

a = 3; b = 0; c = -15;
Δ = b2-4ac
Δ = 02-4·3·(-15)
Δ = 180
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{180}=\sqrt{36*5}=\sqrt{36}*\sqrt{5}=6\sqrt{5}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{5}}{2*3}=\frac{0-6\sqrt{5}}{6}
=-\frac{6\sqrt{5}}{6}
=-\sqrt{5}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{5}}{2*3}=\frac{0+6\sqrt{5}}{6}
=\frac{6\sqrt{5}}{6}
=\sqrt{5}
$