Question

x+y+z=15and x^2+y^2+z^2=77 find the value of xy+ yz+ zx

Answer 1

Hey mate!

Here is your answer > >

x+y+z=15

Squaring both sides

(x+y+z)^2=15^2

x^2+y^2+z^2+2xy+2yz+2zx=225

x^2+y^2+z^2+2 (xy+yz+zx)=225

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

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

2 (xy+yz+zx)=148

(xy+yz+zx)=148/2

(xy+yz+zx)=74

Hope it helps!

Thankyou ☆ ☆

Answer 2

Answer:

74.

Step-by-step explanation:

• ( x + y + z ) ² = x² +y² + z² + 2 ( xy +yz + zx )

⇒ 15² = 77 + 2 (xy + yz +zx )

⇒ 225 - 77 = 2(xy + yz +zx )

⇒ (xy + yz +zx ) = 148/2

∴ (xy + yz +zx ) = 74.