y = - x² - x + 30
a) f(5) = - 5² - 5 + 30 = - 25 - 5 + 30 = 0
f(5) = 0
f(-7) = - (- 7)² - (- 7) + 30 = - 49 + 7 + 30 = - 49 + 37 = - 12
f( - 7) = - 12
b) (k ; 10) ⇒ x = k y = 10
10 = - k² - k + 30
k² + k - 20 = 0
k₁ = - 5 k₂ = 4
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Verified answer
y = - x² - x + 30
a) f(5) = - 5² - 5 + 30 = - 25 - 5 + 30 = 0
f(5) = 0
f(-7) = - (- 7)² - (- 7) + 30 = - 49 + 7 + 30 = - 49 + 37 = - 12
f( - 7) = - 12
b) (k ; 10) ⇒ x = k y = 10
10 = - k² - k + 30
k² + k - 20 = 0
k₁ = - 5 k₂ = 4