SSC CGL 2020 PYQ — Question 72

The correct answer is option 2 i.e - (3/2)

We have given that,

⇒ 4a² + 9b² - 6ab = 13

Squaring both sides,

⇒ (4a² + 9b² - 6ab)² = 169

⇒ 16a⁴ + 81b⁴ + 36a²b² + 2(36a²b² - 24a³b - 54ab³) = 169

By putting the given value,

⇒ 2(36a²b² - 24a³b - 54ab³) = 169 - 91

⇒ 36a²b² - 24a³b - 54ab³ = 39

⇒ -6ab(4a² + 9b² - 6ab) = 39

⇒ -6ab = 39 / 13 = 3

⇒ 3ab = -(3 / 2)