SSC CHSL 2021 PYQ — Question 73

The correct answer is option 2 i.e. -6

Given:

a⁴ + b⁴+ a²b² = 133 and

a² + b² - ab = 19

Concept Used:

(a + b)² = a² + 2ab + b²

Explanation:

According to the given question,

a⁴ + b⁴ + a²b² = 133 

⇒  a⁴ + b⁴ + 2a²b² - a²b² = 133

⇒ (a² + b²)² - a²b² = 133   ....(i)

a² + b² - ab = 19

⇒ a² + b² = 19 + ab   ...(ii)

Now putting value of eqation (ii) in equation (i), we get

⇒  (19 + ab)² - a²b² = 133

⇒ 361 + a²b² + 38ab - a²b² = 133

⇒ 38ab = 133 - 361

⇒ 38ab = -228

⇒ ab = $-228 \over 38$ = -6

Hence the required answer is -6.