CUET · MATHS · PYQ PAPER 2025
If \(y=a x^2+b x\) has minima at \(x=2\) and the minimum value is -12 , then which of the following are correct?
(A) \(a=3\)
(B) \(a=-3\)
(C) \(b=12\)
(D) \(b=-12\)
Choose the correct answer from the options given below :
- A (B) and (C) only
- B (A) and (D) only
- C (A) and (C) only
- D (D) only
Answer & Solution
Correct Answer
(B) (A) and (D) only
Step-by-step Solution
Detailed explanation
\(\frac{dy}{dx} = 2ax + b\) \(2a(2) + b = 0 \Rightarrow 4a + b = 0\) \(a(2)^2 + b(2) = -12 \Rightarrow 4a + 2b = -12\) \(b = -4a\) \(4a + 2(-4a) = -12\) \(4a - 8a = -12\) \(-4a = -12\) \(a = 3\) \(b = -4(3)\) \(b = -12\) Correct options are (A) and (D).
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