a + b + c = 9, ab + bc + ca = 31 হলে, a2 + b2 + c2 = কত ?

A 49

B 39

C 29

D 19

Solution

Correct Answer: Option D

( a + b + c )2 = a2 + b2 + c2 + 2(ab+bc+ca) 
 
⇒ 92 = a2 + b2 + c2 + 2.31 
 
⇒ a2 + b2 + c2 = 81 -62 
 
⇒ a2 + b2 + c2 = 19 

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