As for your last question, that does not tell you very much. It tels you that a is larger than or equal to b which is larger than or equal to c which is larger than 0. A more concise way to express the stipulation is to write
a,b,c \in N
or
a,b,c \in Z^{+}
How did you go from b\frac{a+b}{2}\geq ab to (\frac{a+b}{2})^{2} \geq ab ?
You could just square both the right and left side from the start, so that
0.25a^{2}+0.5ab+0.25b^{2} \geq ab \leftrightarrow 0.25a^{2}+0.25b^{2} \geq 0.5 ab \leftrightarrow a^{2}+b^{2}-2ab \geq 0 \leftrightarrow...
If a and b are relatively prime natural numbers, how many numbers cannot be written on the form xa+yb where x and y are nonnegative integers?
My thoughts:
Let n be a fixed integer such thatn=ax_{0}+by_{0}. Assume that we want to minimize x_{0} but keep it nonnegative. Then the following...