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Identities — MATHS STD 8 — Question

ICSE BoardEnglish MediumSTD 8MATHSIdentities4 Marks
Question
If $a + b + c = 9$ and $ab + bc + ca = 15,$ find$: a^2 + b^2 + c^2.$
✓

Answer

Since $(a + b + c)^2= a^2 + b^2 + c^2 + 2 (ab + bc + ca)$
$\therefore (9)^2 = a^2 + b^2+ c^2 + 2 (15)$
$81 = a^2+ b^2 + c^2 + 30$
$\therefore a^2 + b^2 + c^2= 81 − 30 = 51$

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