If (a − b −c)2 = 49 and bc −ac − ab = 12, then what is the value of the expression a2 + b2 + c2?
25
It is known that: (a − b − c)2 = a2 + b2 + c2 − 2ab + 2bc − 2ac
∴(a − b − c)2 = a2 + b2 + c2 + 2 (bc − ac − ab)
⇒ a2 + b2 + c2 = (a − b − c)2 − 2 (bc − ac − ab)
= 49 − 2(12) [(a − b −c)2 = 49, bc −ac − ab = 12]
= 25