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 #3
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If x, y, w, z are real numbers satisfying
 
w+x+y=2w+x+z=4w+y+z=19x+y+z=12

 

What is wx+yz?

 

(1)w+x+y=2(2)w+x+z=4(3)w+y+z=19(4)x+y+z=12(1)+(2)+(3)+(4):3w+3x+3y+3z=2+4+19+123(w+x+y+z)=33|:3w+x+y+z=11

 

w+x+y+z=11|x+y+z=12w+12=11w=1112w=1w+x+y+z=11|w+y+z=19x+19=11x=1119x=8w+x+y+z=11|w+x+z=4y+4=11y=114y=7w+x+y+z=11|w+x+y=2z2=11z=11+2z=13

 

wx+yz=(1)(8)+713=8+91wx+yz=99

 

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Jun 15, 2021
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Jun 15, 2021

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