-2/5y-1/8y=840

Solution for -2/5y-1/8y=840 equation:

-2/5y-1/8y=840

We move all terms to the left:

-2/5y-1/8y-(840)=0


Domain of the equation: 5y!=0

y!=0/5

y!=0

y∈R



Domain of the equation: 8y!=0

y!=0/8

y!=0

y∈R


We calculate fractions


(-16y)/40y^2+(-5y)/40y^2-840=0

We multiply all the terms by the denominator


(-16y)+(-5y)-840*40y^2=0

Wy multiply elements

-33600y^2+(-16y)+(-5y)=0

We get rid of parentheses

-33600y^2-16y-5y=0

We add all the numbers together, and all the variables

-33600y^2-21y=0

a = -33600; b = -21; c = 0;
Δ = b2-4ac
Δ = -212-4·(-33600)·0
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-21}{2*-33600}=\frac{0}{-67200}
=0
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+21}{2*-33600}=\frac{42}{-67200}
=-1/1600
$