You can use the quadratic formula for an equation of the form a*x^2 + b*x + c = 0.
x = (-b +/- sqrt(b^2-4*a*c))/(2*a)
In this case:
a = 1
b = -3
c = -28
x = (3 +/- sqrt(9 - 4*(-28)))/2
x = (3 +/- sqrt(121))/2
x = (3 +/- 11)/2
x = 7 or -4
Another option is to attempt to simplify the equation into the form (x-a)(x-b) = 0.
Sometimes you can do this by observation.
For example:
28 = 4*7
7-4 = 3
Thus:
(x-7)(x+4)=0
In this case, a and b are known as the "roots" of the equation, with a = 7 and b = -4.
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x: x2 - 81 = 0
y=±√15
16
4n2-25 = 0 4n2=25 n2=6.25 n=sqrt(6.25) n= +2.5 or -2.5
In order to solve this equation you need to know what -28x-2 equals. If you were to assume it was 0 then x = 0.071 rounded