Quadratic equation
Quadratic equation is given in the form:
ax2 + bx + c = 0,
where ‘a’, ‘b’ and ‘c’ are constants and a ≠ 0.
The solution to this quadratic equation is given by the following quadratic formula:
Here b2 – 4ac is called as discriminant.
If b2 – 4ac > 0, then the equation has two solutions.
If b2 – 4ac = 0, then the equation has one solution.
If b2 – 4ac < 0, then the equation has no real solutions.
Using quadratic equation, it is possible to find the value of ‘x’, if ‘a’, ‘b’ and ‘c’ are known. For example, consider a 2nd order polynomial equation:
y = ax2 + bx + c.
By using quadratic formula, it is possible to determine the value of ‘x’ data when, y = 0.
If y = 0, then 2nd order polynomial equation becomes a quadratic equation as,
0 = ax2 + bx + c when a ≠ 0.
Example #1
In an experimental analysis, for a set of ‘x’ and ‘y’ data, the derived 2nd order polynomial curve fit equation is:
y = 2x2 – 9x + 10.
Determine the value of ‘x’ when y = 0.
Solution
In this a = 2; b = –9 and c = 10. From this it is possible to determine ‘x’ when y = 0, and the equation becomes quadratic form: 0 = 2x2 – 9x + 10.
Hence ‘x’ can have
two values such as:
So the equation, y = 2x2 – 9x + 10 = 0;
at x = 2.0 or x = 2.5.
y = (2 × 2.52) – (9 × 2.5) + 10 = 0
y = (2 × 2.0 2) – (9 × 2.0) + 10 = 0
Example #2
An experimental result obeys the following 2nd order equation, y = 2x2 – 8x + 8. Determine the value of ‘x’ at y = 0.
Solution
This equation becomes quadratic equation when y = 0.
2x2 – 8x + 8 = 0
In this a = 2, b = –8 and c = 8. The value of ‘x’ can be determined from the quadratic formula as:
So, the value of ‘x’ = 2 when y = 0.
y = 2x2 – 8x + 8 = 0 at x = 2
y = (2 × 22) – (8 × 2) + 8 = 0
It should be emphasized that, in the equation: 2x2 – 9x + 10 = 0, as given in the Example #1, the value of (b2 – 4ac) > 0 and hence it has two solutions or two ‘x’ values.
But in Example #2, the quadratic equation, 2x2 – 8x + 8 = 0 has only one solution, since the value of (b2 – 4ac) = 0.