Is (1,2) a solution of the system y>2x and x+y< 3

Answer: No it is not a solution

Why not? Because it doesn't make the first inequality true. Replace x with 1 and y with 2

y > 2x

y > 2*1 ... replaced x with 1

2 > 2*1 ... replaced y with 2

2 > 2 ... which is a false inequality statement since 2 is not larger than itself

Answer: NO!

Step-by-step explanation:

x = 1, y = 2

y > 2x

2 > 2 (1)

2 > 2

False

Sine it already failed, no need to check the other equation.