Find the minimum value of the polynomial 2 x 2 − 3 x + 4 for real x .
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Good idea but you can use direct formula which is derived using graph or by completing the square
The minimum value is given by 4 a − D using the graph
= 4 a 4 a c − b 2
= 8 3 2 − 9
= 8 2 3
Use formula for vertex of parabola of polynomial
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The minimum value can be easily determined by completing the square:
2 x 2 − 3 x + 4 = 2 ( x 2 − 2 3 x ) + 4 = 2 ( x − 4 3 ) 2 − 2 × ( 4 3 ) 2 + 4 =
= 2 ( x − 4 3 ) 2 − 8 9 + 4 = 2 ( x − 4 3 ) 2 + 8 2 3
The latter expression is minimal, when the square is zero ( x = 0.75 ).
Hence, the minimum value is:
8 2 3