If a + b + c = 7 and a3 + b3 + c3 - 3abc = 301, then ab + bc + ca = ?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 2.
a3 + b3 + c3 - 3abc = (a + b + c)[(a + b + c)2 - 3(ab + bc + ca)]
⇒ 301 = 7[49 - 3(ab + bc + ca)]
⇒ 43 - 49 = - 3(ab + bc + ca)
⇒ 2 = (ab + bc + ca)