If a+b+c=6 and a^2+b^2+c^2=20, find ab+bc+ca.
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a^2 + b^2 + c^2 = 20 -------(1)
a + b + c = 6
On squaring both sides, we get
a^2 + b^2 + c^2 + 2ab + 2bc + 2ca = 36
=> 20+ 2 ( ab + bc + ca) = 36
=> 2 ( ab + bc + ca) = 16
=> ab + bc + ca = 8
a + b + c = 6
On squaring both sides, we get
a^2 + b^2 + c^2 + 2ab + 2bc + 2ca = 36
=> 20+ 2 ( ab + bc + ca) = 36
=> 2 ( ab + bc + ca) = 16
=> ab + bc + ca = 8
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