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If the minimum value of f(x)=x2+2bx+2c2f(x) = x^2 + 2bx + 2c^2 is greater than the maximum value of g(x)=−x2−2cx+b2g(x) = -x^2 - 2cx + b^2, then for real value of x.

Solution

✅ Correct Option: 1

For quadratic function f(x)=x2+2bx+2c2f(x) = x^2 + 2bx + 2c^2:

  • Minimum value occurs at x=−bx = -b (coefficient of xx divided by -2)
    • Minimum value = f(−b)=b2+(−2b2)+2c2=2c2−b2f(-b) = b^2 + (-2b^2) + 2c^2 = 2c^2 - b^2

For quadratic function g(x)=−x2−2cx+b2g(x) = -x^2 - 2cx + b^2:

  • Maximum value occurs at x=−cx = -c (coefficient of xx divided by -2)
    • Maximum value = g(−c)=−c2+2c2+b2=c2+b2g(-c) = -c^2 + 2c^2 + b^2 = c^2 + b^2

Given that minimum of f(x)f(x) > maximum of g(x)g(x):

2c2−b2>c2+b22c^2 - b^2 > c^2 + b^2

2c2−c2>b2+b22c^2 - c^2 > b^2 + b^2

c2>2b2c^2 > 2b^2

∣c∣>2∣b∣|c| > \sqrt{2}|b|

Therefore, ∣c∣>2∣b∣|c| > \sqrt{2}|b| is the correct condition.

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