Question

if a^2+b^2+c^2=20 and a+b+c=9 find ab+bc+ca =____________​

Answer 1

Answer:

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Step-by-step explanation:

Answer 2

a+b+c=9

=>(a+b+c)²=9²

{squre both side , to apply formula of (a+b+c)² }

=> a² + b² + c² + 2ab + 2bc + 2ca.=81

{ replace value of a² + b² + c²}

=>20 +2(ab+bc+ca)= 81

=>ab+bc+ca = (81-20)/2

=> ab+bc+ca = 30.5

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