Question

Is 2x + y2=5 a function?

Answer 1

y=x2−4x−5=(x2−4x+4)−9=(x−2)2−9y=x2−4x−5=(x2−4x+4)−9=(x−2)2−9, now as (x−2)2≥0(x−2)2≥0 (so min value is 0) then the minimum value of the function is 0-9=-9.