Put the terms in order of decreasing degree, all on the left. When convenient, it is nice to have mutually prime integer coefficients with the leading one positive.
a) x² -2x +1 = 0
b) x² +15 = 0
c) 4x² -12 = 0
or, better, divide out the common factor of 4.
x² -3 = 0
d) 3x² -x -5 = 0
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Shown is the standard form for a single-variable second-degree equation. Form varies depending on the nature of the equation. Equations of conic sections have different standard forms, depending on the curve.