Question

x+y+z=15
xy+yz+zx =?
x² + y2 +z2


= 77​

Answer 1

Answer:

(x+y+z)²=x²+y²+z²+2(xy+yz+zx)

(15)²=77+2(xy+yz+zx)

225=77+2(xy+yz+zx)

225-77=148=2(xy+yz+zx)

148/2=74=xy+yz+zx

74=xy+yz+zx

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