a+b+c=9 , ab + bc + ca =31 হলে , a2+b2+c2 = কত?
A
49
B
39
C
29
D
19
Correct Answer: 19
a + b + c = 9, ab + bc + ca = 31, a² + b² + c² = ? (a + b + c)² = a² + b² + c² + 2(ab + bc + ca) বা, a² + b² + c² = (a + b + c)² - 2(ab + bc + ca) = 9² - (2×31) = 81 - 62 = 19