Question

If a + b = 11 and ab = 15, then $a^2 + b^2$ is equal to:

• A. 90
• B. 91
• C. 93
• D. 92

Answer 1

Answer:

B. 91

Given:

a + b = 11 and ab = 15

Formula:

(a + b)² = a² + b² + 2ab

Calculation:

$(a+b)^2=a^2+b^2+2ab$

⇒ $11^2=a^2+b^2+2\times{15}$

⇒ a² + b² = 121 - 30

∴ a² + b² = 91