If a + b + c = p and ab + bc + ca = q; find a2 + b2 + c2.
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By formula,
(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc + ca).
Substituting values we get :
⇒ p2 = a2 + b2 + c2 + 2q
⇒ a2 + b2 + c2 = p2 - 2q.
Hence, a2 + b2 + c2 = p2 - 2q.
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