ecuatia dreptei este ecuatie de forma f(x)=ax+b
Daca A(2,3) apartine dreptei => f(2)=3=>a*2+b=3=>b=3-2a
Daca B(-5,4) apartine dreptei => f(-5)=4=>a*(-5)+b=4 dar b=3-2a=>-5a+3-2a=4
=>-7a=4-3=>a=-1/7 dar b=3-2a=>b=3+2/7=(21+2)/7=23/7
f(x)=-1/7x+23/7 sa verificam
f(2)=-2/7+23/7=21/7=3
f(-5)=5/7+23/7=28/7=4
