Can an equation be considered standard form if it has more than 3 terms
for example is this considered standard form?
21x^3+6x^2-43x+20
also can standard form contain fractions?
for example
2x+3+[11/(x-3)]
yes, standard form for a polynomial can have more than three forms.
http://www.mathwarehouse.com/dictionary/S-words/definition-of-standard-form-of-a-polynomial.php
your second example, no, that is not standard form.
How would I write the second one in standard form then?
Yes, an equation can be considered standard form even if it has more than 3 terms. The standard form of an equation refers to a specific arrangement of terms in descending order of degree. In your example, the equation 21x^3+6x^2-43x+20 is indeed in standard form because the terms are ordered from highest degree to lowest degree: 21x^3, 6x^2, -43x, and 20.
Regarding your second question, standard form typically does not include fractions. In the equation 2x+3+[11/(x-3)], the term 11/(x-3) is not in standard form because it contains a fraction. However, you can rewrite the equation to eliminate the fraction and put it in standard form.