Nilai f(1) untuk f(y) = -y² + 4xy + 5x² ,jika diketahui bahwa ½ log (2x²-x-2) = log (x+2)

jawab
1/2  log (2x² -  x - 2) = log (x+2)
(2x² - x - 2)^(1/2) = (x + 2)  | pangkatkan 2
{(2x² - x -2)^(1/2)}² = (x+2)²
(2x² - x  - 2 )¹ = (x+2)²
2x² - x - 2 = x² + 4x + 4
2x² - x² - x - 4x - 2 - 4 = 0
x² - 5x - 6 = 0
(x - 6)(x + 1) = 0
x = 6  atau x = - 1

f(y) = - y² + 4 xy + 5x²
x = 6 → f(y) =  -y² + 4(6)y + 5(6)²
f(y) = -y² + 24y + 180
f(1) = -(1)² + 24(1) + 180
f(1) = -1 + 24 + 180 = 203

x = - 1→ f(y) = -y² + 4(-1)y + 5(-1)²
f(y) = -y² - 4y + 5
f(1) = -(1)² - 4 (-1) + 5
f(1) = -1 + 4 + 5 = 8