Which number from the set {1, 2, 3,4} makes the inequality 5x² > 12x + 9 true for x? Is it 1 or 2 or 3 or 4?

Question

is it 1 or 2 or 3 or 4?

Answer 1

It's 4 and only 4

5(4)^2 = 5(16)= 80 > 12(4)+9 = 48+9 =57

80>57

plug in 1, 2 or 3 and you get

5(1)^2= 5 < 12(1)+9= 21

5<21

5(2)^2 = 20<12(2)+9 = 33

20<33

5(3)^2 =45 < 12(3)+9=36+9=45

45=45