62. If a2+ b2 + c2 = 21, and a + b + c = 7, then (ab + bc +
ca) is equal to:
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ab + bc + ca = 14
Step-by-step explanation:
Given
a² + b² + c² = 21
a + b + c = 7
ab + bc + ca = ?
(a + b + c)² = a² + b² + c² 2(ab + bc + ca)
(7)² = 21 + 2(ab + bc + ca)
2(ab + bc + ca) = 49 - 21
ab + bc + ca = 28/2
ab + bc + ca = 14
Hope it's help you!
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