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secondary 4 | A Maths
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Date Posted: 4 years ago
Views: 180
y = x³ + 4x² + kx + 3
dy/dx = 3x² + 8x + k
When the curve is an increasing function,
dy/dx > 0
So 3x² + 8x + k > 0
dy/dx = 3x² + 8x + k
When the curve is an increasing function,
dy/dx > 0
So 3x² + 8x + k > 0
3x² + 8x + k > 0
This means the curve of 3x² + 8x + k will never be lower or equal to 0. So it will not have any intersection with the line y = 0
So there's no real roots for 3x² + 8x + k = 0
Discriminant < 0
(b² - 4ac)
8² - 4(3)(k) < 0
64 - 12k < 0
12 k > 64
k > 64/12
k > 5⅓
This means the curve of 3x² + 8x + k will never be lower or equal to 0. So it will not have any intersection with the line y = 0
So there's no real roots for 3x² + 8x + k = 0
Discriminant < 0
(b² - 4ac)
8² - 4(3)(k) < 0
64 - 12k < 0
12 k > 64
k > 64/12
k > 5⅓
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