Verified Solution • 2025–26 Session moderate

QJEEM24Maffd0: JEE Main 2024 Mathematics - Class 12 JEEM24Maffd0 Solution: Let be such that and . Then is equal to:

Let f(x)=ax3+bx2+cx+41f(x)=a x^3+b x^2+c x+41 be such that f(1)=40,f′(1)=2f(1)=40, f^{\prime}(1)=2 and f′′(1)=4f^{\prime \prime}(1)=4 . Then a2+b2+c2a^2+b^2+c^2 is equal to:

Multiple Choice Options

  • A 54
  • B 51
  • C 73
  • D 62

Step-by-Step Verified Solution

Given the polynomial function:

f(x)=ax3+bx2+cx+41f(x) = ax^3 + bx^2 + cx + 41

We are provided the following conditions from the problem:

1. f(1)=40f(1) = 40

2. f′(1)=2f^{\prime}(1) = 2

3. f′′(1)=4f^{\prime \prime}(1) = 4

First, calculate f(1)f(1) :

f(1)=a(1)3+b(1)2+c(1)+41=40f(1) = a(1)^3 + b(1)^2 + c(1) + 41 = 40

Simplifying, we get:

a+b+c+41=40a + b + c + 41 = 40

Therefore:

a+b+c=−1a + b + c = -1

Next, calculate the first derivative f′(x)f^{\prime}(x) :

f′(x)=3ax2+2bx+cf^{\prime}(x) = 3ax^2 + 2bx + c

Given f′(1)=2f^{\prime}(1) = 2 :

f′(1)=3a(1)2+2b(1)+c=2f^{\prime}(1) = 3a(1)^2 + 2b(1) + c = 2

Simplifying, we get:

3a+2b+c=23a + 2b + c = 2

Next, calculate the second derivative f′′(x)f^{\prime \prime}(x) :

f′′(x)=6ax+2bf^{\prime \prime}(x) = 6ax + 2b

Given f′′(1)=4f^{\prime \prime}(1) = 4 :

f′′(1)=6a(1)+2b=4f^{\prime \prime}(1) = 6a(1) + 2b = 4

Simplifying, we get:

6a+2b=46a + 2b = 4

Dividing the entire equation by 2:

3a+b=23a + b = 2

We now have three equations:

1. a+b+c=−1a + b + c = -1

2. 3a+2b+c=23a + 2b + c = 2

3. 3a+b=23a + b = 2

To solve for aa , bb , and cc , follow these steps:

First, subtract the third equation from the second equation:

(3a+2b+c)−(3a+b)=2−2(3a + 2b + c) - (3a + b) = 2 - 2

Which simplifies to:

b+c=0b + c = 0

So,

c=−bc = -b

Substitute c=−bc = -b into the first equation:

(a+b−b=−1)(a + b - b = -1)

Simplifying, we get:

a=−1a = -1

Now substitute a=−1a = -1 into the third equation:

3(−1)+b=23(-1) + b = 2

Which simplifies to:

−3+b=2-3 + b = 2

Therefore:

b=5b = 5

Next, since c=−bc = -b :

c=−5c = -5

Finally, we need to find a2+b2+c2a^2 + b^2 + c^2 :

a2+b2+c2=(−1)2+52+(−5)2a^2 + b^2 + c^2 = (-1)^2 + 5^2 + (-5)^2

Simplifying, we get:

1+25+25=511 + 25 + 25 = 51

Therefore, the answer is:

Option B: 51

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