NIMCET 2010 — Mathematics PYQ
NIMCET | Mathematics | 2010If y=alogx+bx2+x has its extremum value at x=−1 and x=2, then:
Choose the correct answer:
- A.
a=2,b=−1
- B.
a=−2,b=21
a=2,b=−21
Explanation
Step 1: Find the first derivative of the function.
Given:
Differentiating with respect to x:
Step 2: Apply the condition for extremum values.
Extremum values occur where the derivative is zero (dxdy=0).
-
At x=2:
2a+2b(2)+1=02a+4b+1=0⟹a+8b=−2…(Equation 1) -
At x=−1 (Assuming the formal derivative must vanish):
−1a+2b(−1)+1=0−a−2b+1=0⟹a+2b=1…(Equation 2)
Step 3: Solve the system of linear equations.
Subtract Equation 2 from Equation 1:
Now, substitute b=−21 into Equation 2:
Step 4: Conclusion.
The values are a=2 and b=−21.
Explanation
Step 1: Find the first derivative of the function.
Given:
Differentiating with respect to x:
Step 2: Apply the condition for extremum values.
Extremum values occur where the derivative is zero (dxdy=0).
-
At x=2:
2a+2b(2)+1=02a+4b+1=0⟹a+8b=−2…(Equation 1) -
At x=−1 (Assuming the formal derivative must vanish):
−1a+2b(−1)+1=0−a−2b+1=0⟹a+2b=1…(Equation 2)
Step 3: Solve the system of linear equations.
Subtract Equation 2 from Equation 1:
Now, substitute b=−21 into Equation 2:
Step 4: Conclusion.
The values are a=2 and b=−21.
