42=1.4r2

Solution for 42=1.4r2 equation:

42=1.4r^2

We move all terms to the left:

42-(1.4r^2)=0

We get rid of parentheses

-1.4r^2+42=0

a = -1.4; b = 0; c = +42;
Δ = b2-4ac
Δ = 02-4·(-1.4)·42
Δ = 235.2
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-\sqrt{235.2}}{2*-1.4}=\frac{0-\sqrt{235.2}}{-2.8}
=-\frac{\sqrt{}}{-2.8}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{235.2}}{2*-1.4}=\frac{0+\sqrt{235.2}}{-2.8}
=\frac{\sqrt{}}{-2.8}
$