In the following example, we want students to type in the expression \(a x^2 + b x + c\), but where \(a\), \(b\) and \(c\) are numeric constants, for example \(7 x^2 + 4 x + 6\) where \(7\), \(4\) and \(6\) are, say, calculated in previous steps.
We don't want students to be able to enter \(a x^2 + b x + c\). We therefore carry out a change of variables locally in the parts, for example we define a_zkd = a where a_zkd is a name made up of "\(a\)" followed by random characters so that students cannot guess and use this name, then we define locally, i.e. temporarily, a, b and c to incorrect values. This way the only correct answers are 7 x^2 + 4 x + 6 and a_zkd x^2 + b_asq x + c_mch. Obviously, the only correct answer students could give is the first one.
The following question consists of two parts which use the global variables \(a\), \(b\) and \(c\), in order to demonstrate that the redefinition of these variables in the parts is indeed local and therefore that it does not affect the global values.
Note that a regular space can replace the multiplication sign. Students can therefore enter 7*x^2 + 4*x + 6 or 7 x^2 + 4 x + 6, the second way being probably easier.
Algebraic formula answer type-20211014-1614.xml