Quadratic Equation are equations where the highest power of the variable (usually x) is 2, hence the word Quadratic Equations
The standard form of Quadratic Equations is as follows...
This is because, even with an equation such as x^2 = 5, you can always* change it to the standard form.
There! We got 1x^2 + 0x - 5 = 0!
You can cross check it with the standard form and see its the same!
Did you wonder why "a" can't be zero in the standard form? Well look here.
At first glance, one may not notice the issue but let me pin point the definition of Quadratic Equation...
"Quadratic Equation are equations where the highest power of the variable is 2"
The definition states the highest power of x should be 2 but in 10x + 20 = 0 the highest power is 1 (where is no power, there is 1) so this equation became a linear equation! so to prevent that is why "a" or the coefficient of "x^2" can't equal to 0 in a Quadratic Equation
thank u! <3
NOW GO LEARN
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* = take with a pinch of salt