Question


Answer

a+b+2c=1

(a+b)^2=(1-2c)^2


a^2+b^2+2ab=4c^2-4c+1
(1)

a^2+b^2-8c^2+6c=5
(2)

Subtract expressions: (1) - (2) , we get,

2ab = -4c^2+2c-4

ab=-2c^2+c-2

\therefore ab-bc-ca

=-2c^2+c-2 - c(a+b)

=-2c^2+c-2 - c(1-2c)

=-2c^2+c-2 - c+2c^2

=-2

Steven Zheng posted 3 months ago

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