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{{ printedBook.courseTrack.name }} {{ printedBook.name }} A quadratic equation can be written in the form $ax^2+bx+c=0,$ that is, it contains one unknown, at least one $x^2$-term as well as an equal sign. This means that $\mathbf{D:} \ x^2=25 \quad \text{and} \quad \mathbf{F:} \ x^2+2x-30=0$ are quadratic equations. $y=x^2+3$ has two unknowns, $x$ and $y$ and is therefore a quadratic function. In the first equation, there is no $x^2$-term. Instead the integer $7$ is squared, which is another way to write $49.$ $10x^2-8+2x$ is an algebraic expression since it lacks the equal sign.