Solved on Feb 07, 2024

Find the linear operator from P3P_3 to P4P_4 where L(p(x))=x2p(x)+p(x)+p(0)L(p(x)) = x^2 p''(x) + p'(x) + p(0).

STEP 1

Assumptions
1. P3P_{3} denotes the space of polynomials of degree at most 3.
2. P4P_{4} denotes the space of polynomials of degree at most 4.
3. A linear operator LL from P3P_{3} to P4P_{4} must satisfy the following properties for all p(x),q(x)P3p(x), q(x) \in P_{3} and scalars a,bRa, b \in \mathbb{R}: - Linearity: L(ap(x)+bq(x))=aL(p(x))+bL(q(x))L(ap(x) + bq(x)) = aL(p(x)) + bL(q(x))
4. p(x)p'(x) denotes the first derivative of p(x)p(x) with respect to xx.
5. p(x)p''(x) denotes the second derivative of p(x)p(x) with respect to xx.

STEP 2

We will check each given operator to see if it satisfies the linearity properties. The operator that satisfies these properties is the linear operator we are looking for.

STEP 3

Test the first operator L(p(x))=x2p(x)p(x)+p(0)L(p(x))=x^{2} p^{\prime \prime}(x) p^{\prime}(x)+p(0) for linearity.

STEP 4

Check if L(ap(x)+bq(x))=aL(p(x))+bL(q(x))L(ap(x) + bq(x)) = aL(p(x)) + bL(q(x)) holds for the first operator.

STEP 5

Calculate L(ap(x)+bq(x))L(ap(x) + bq(x)) using the first operator.
L(ap(x)+bq(x))=x2(ap(x)+bq(x))((ap(x)+bq(x)))+(ap(x)+bq(x))(0)L(ap(x) + bq(x)) = x^{2} (ap(x) + bq(x))^{\prime \prime} ((ap(x) + bq(x))^{\prime}) + (ap(x) + bq(x))(0)

STEP 6

Observe that the expression involves products and compositions of functions, which are not linear operations. Therefore, the first operator is not linear.

STEP 7

Test the second operator L(p(x))=p(x)p(x)L(p(x))=p^{\prime}(x) p^{\prime \prime}(x) for linearity.

STEP 8

Check if L(ap(x)+bq(x))=aL(p(x))+bL(q(x))L(ap(x) + bq(x)) = aL(p(x)) + bL(q(x)) holds for the second operator.

STEP 9

Calculate L(ap(x)+bq(x))L(ap(x) + bq(x)) using the second operator.
L(ap(x)+bq(x))=(ap(x)+bq(x))(ap(x)+bq(x))L(ap(x) + bq(x)) = (ap(x) + bq(x))^{\prime} (ap(x) + bq(x))^{\prime \prime}

STEP 10

Observe that the expression involves products of derivatives, which are not linear operations. Therefore, the second operator is not linear.

STEP 11

Test the third operator L(p(x))=xp(x)L(p(x))=x p(x) for linearity.

STEP 12

Check if L(ap(x)+bq(x))=aL(p(x))+bL(q(x))L(ap(x) + bq(x)) = aL(p(x)) + bL(q(x)) holds for the third operator.

STEP 13

Calculate L(ap(x)+bq(x))L(ap(x) + bq(x)) using the third operator.
L(ap(x)+bq(x))=x(ap(x)+bq(x))L(ap(x) + bq(x)) = x (ap(x) + bq(x))

STEP 14

Distribute xx across the sum.
L(ap(x)+bq(x))=axp(x)+bxq(x)L(ap(x) + bq(x)) = axp(x) + bxq(x)

STEP 15

Observe that this expression can be written as aL(p(x))+bL(q(x))aL(p(x)) + bL(q(x)), which satisfies the linearity condition. Therefore, the third operator is linear.

STEP 16

Since we have found a linear operator, we do not need to test the remaining operators. The linear operator from P3P_{3} to P4P_{4} is:
L(p(x))=xp(x)L(p(x))=x p(x)

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