How do you solve x2-3x-28 equals 0?

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.