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

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A90

B91

C93

D92

Answer:

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

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