Question

Does the point (25,75) lie on the straight line y=3x. How do you know that

Answer 1

$75=3\cdot25\\ 75=75 \Rightarrow \hbox{It does.}$

Answer 2

$y=3x \\ \\ x=25 \\ y=75 \\ \\ 75= 3*25 \\ 75=75->OK$