85=(2x+10)(4x-15)

Solution for 85=(2x+10)(4x-15) equation:

85=(2x+10)(4x-15)

We move all terms to the left:

85-((2x+10)(4x-15))=0

We multiply parentheses ..

-((+8x^2-30x+40x-150))+85=0


We calculate terms in parentheses: -((+8x^2-30x+40x-150)), so:

(+8x^2-30x+40x-150)

We get rid of parentheses

8x^2-30x+40x-150

We add all the numbers together, and all the variables

8x^2+10x-150

Back to the equation:

-(8x^2+10x-150)


We get rid of parentheses

-8x^2-10x+150+85=0

We add all the numbers together, and all the variables

-8x^2-10x+235=0

a = -8; b = -10; c = +235;
Δ = b2-4ac
Δ = -102-4·(-8)·235
Δ = 7620
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{7620}=\sqrt{4*1905}=\sqrt{4}*\sqrt{1905}=2\sqrt{1905}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-2\sqrt{1905}}{2*-8}=\frac{10-2\sqrt{1905}}{-16}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+2\sqrt{1905}}{2*-8}=\frac{10+2\sqrt{1905}}{-16}
$