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What two numbers add to 8 and multiply to 28

User Kyle Butt
by
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1 Answer

6 votes
find numbers that multiply to 28 and add them to see if they add to 8
28=
1 and 28=29 not 8
2 and 14=16 not 8
4 and 7=11 not 8
that's it'
no 2 numbers
we must use quadratic formula

x+y=8
xy=28

x+y=8
subtract x fromb oths ides
y=8-x
subsitute
x(8-x)=28
distribute
8x-x^2=28
add x^2 to both sides
8x=28+x^2
subtract 8x
x^2-8x+28=0

if you have
ax^2+bx+c=0 then x=
\frac{-b+/- \sqrt{b^(2)-4ac} }{2a}
so if we have
1x^2-8+28=0 then
a=1
b=-8
c=28

x=
\frac{-(-8)+/- \sqrt{(-8)^(2)-4(1)(28)} }{2(1)}
x=
(8+/- √(-48) )/(2)
x=
(8+/- 4 √(-3) )/(2)
x=
4+/- 2 √(-3)
x=
4+/- 2i √(3)
there are no real numbers that satisfy this
User TGM
by
8.5k points

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