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what are two numbers that multiply to 64 and add to - 20

Sagot :

semsee45

Answer:

-4 and -16

Step-by-step explanation:

Let x = first number

Let y = second number

Given:

  • The two numbers multiply to 64

⇒ xy = 64

Given:

  • The two numbers add to -20

⇒ x + y = -20

Rewrite  x + y = -20  to make x the subject:

⇒ x = -20 - y

Substitute into xy = 64 and solve for y:

⇒ (-20 - y)y = 64

⇒ -20y - y² = 64

⇒ y² + 20y + 64 = 0

⇒ (y + 4)(y + 16) = 0

⇒ y = -4, y = -16

As x + y = -20

If y = -4 then x = -16

If y = -16 then x = -4

Therefore, the two numbers are -4 and -16

Let they be a and b

  • a+b=-20--(1)
  • ab=64

So

[tex]\\ \rm\rightarrowtail (a-b)^2=(a+b)^2-4ab[/tex]

[tex]\\ \rm\rightarrowtail (a-b)^2=(-20)^2-4(64)=400-256=144[/tex]

[tex]\\ \rm\rightarrowtail a-b=12\dots(2)[/tex]

From both equations

  • 2a=-8=>a=-4
  • -4+b=-20
  • b=-16
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