Question

If x+y+z=10 and x^2 +y^2 +z^2=40 . Find xy +yz +xz .

Answer 1

Answer:

(x+y+z)²=x²+y²+z²+2(xy+yz+zx)

10²=40+2(xy+yz+zx)

2(xy+yz+zx)=100-40=60

xy+yz+zx=30

Answer 2

Answer:

(x+y+z)^2=x^2+y^2+z^2+2xy+2yz+2xz

So from  ur given question :

(10)^2=40+2(xy+yz+zx)

=>60=2(xy+yz+zx)

Therefore xy+yz+zx=30 !!

Hope u get this!!

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