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 Quadratic equations can be identified by the degree of an equation. If the degree of an equation is 2, then it is a quadratic equations. But some expressions are there, which, on simplifying, are found out to have a degree other than 2. For example, simplifying the following expression, we get: 3x^2(x  +  2) = 3x^3 + 6x^2 The degree of the expression can only be correctly determined after simplifying it. The degree of the above expression appears to be 2 but on expanding it we find that its degree is 3. Therefore we always should simplify an expression/equation before concluding whether it is quadratic or not.
Identify whether the following is a quadratic expression or not:
2x + 3x(3 + x)
Solution: The above expression on simplifying gives:
2x + 3x*3 + 3x*x
2x + 9x + 3x^2
The degree of the last expression is 2 and thus it is a quadratic expression. Thus the expression 2x + 3x(3 + x) is a quadratic expression.

Exercise: Identify whether the following are quadratic expression or not:
1. 3x + 4x^2
2. 8x^2 (2 + x)
3. 3x(x + x^2)
Solutions:
1. Yes it is a quadratic expression.
2. No this is not a quadratic expression.
3. No this is not a quadratic expression.