sqrt x^2 = − x is true for?

√x, like any function, is "single valued". That's part of the definition of function: for any specific value of x, f(x) must be a single value. It is true that, for example, x2=4 has two roots: x= -2 and x= 2. But √4 is specifically defined as "the non-negative number whose square is 4". More generally √a is defined as "the non-negative number whose square is a". In fact, the reason why we have to write the solutions to x2=a as "±√a" is because √a alone does NOT include "± ".

Step-by-step explanation:

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b) the dogs need to shift their focus to human scent.