$(x,y)$
$(0,81)$
$(1,80)$
$(2,77)$

Which of the following equations describes $y$ in terms of $x$ for all ordered pairs in the table above?

เฉลยละเอียด

[STEP]Try substitue $x$ and $y$ from the ordered pairs into each choice[/STEP]

Substitue $x=0$ and $y=81$ from $(0,81)$

$81=81-0^2 A) ok
$81=81-0$ B) ok
$81=81-2(0)$ C) ok
$81=81-4(0)$ D) ok
$81=81-81(0)$ E) ok

Substitue $x=1$ and $y=80$ from $(1,80)$

$80=81-1^2$ A) ok
$80=81-1$ B) ok
$80=81-2(1)$ C) wrong!
$80=81-4(1)$ D) wrong!
$80=81-81(1)$ E) wrong!

Substitue $x=2$ and $y=77$ from $(2,77)$

$77=81-2^2$ A) ok
$77=81-2$ B) wrong!

Therefore the correct answer is A)

[ANS]$y=100-x^2$[/ANS]

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