Ex 3.8

Discover the Magic of Polynomial Square Roots ✨

(x + y)² = x² + 2xy + y²

Division Method for Square Roots

Let's learn how to find square roots of polynomials step by step!

Step 1: Arrange the Polynomial

Make sure the polynomial is arranged in descending order of exponents. If any term is missing, use a 0 coefficient as a placeholder.

Step 2: Pair the Terms

Starting from the right, pair the terms in groups of two. For odd-degree polynomials, the leftmost term will be alone.

Step 3: Find the Square Root

Similar to numerical square roots, find terms that when squared and subtracted, bring down the next pair.

Step 4: Continue the Process

Double the current result, find the next digit, multiply, subtract, and bring down until all terms are exhausted.

Step 5: Verify

Multiply your result by itself to verify it matches the original polynomial.

Problem 1: Find Square Roots

(i) x⁴ − 12x³ + 42x² − 36x + 9

Solution for (i):

1. Polynomial is already in descending order: x⁴ − 12x³ + 42x² − 36x + 9

2. Find square root:

___________ x² - 6x + 3 | x⁴ - 12x³ + 42x² - 36x + 9 x⁴ --------- -12x³ + 42x² -12x³ + 36x² ------------ 6x² - 36x + 9 6x² - 36x + 9 ------------ 0

3. Verification: (x² - 6x + 3)² = x⁴ - 12x³ + 42x² - 36x + 9 ✓

∴ √(x⁴ − 12x³ + 42x² − 36x + 9) = x² - 6x + 3

(ii) 37x² − 28x³ + 4x⁴ + 42x + 9

Solution for (ii):

1. Rearrange in descending order: 4x⁴ - 28x³ + 37x² + 42x + 9

2. Find square root:

___________ 2x² - 7x - 3 | 4x⁴ - 28x³ + 37x² + 42x + 9 4x⁴ --------- -28x³ + 37x² -28x³ + 49x² ------------ -12x² + 42x + 9 -12x² + 42x + 9 --------------- 0

3. Verification: (2x² - 7x - 3)² = 4x⁴ - 28x³ + 37x² + 42x + 9 ✓

∴ √(4x⁴ - 28x³ + 37x² + 42x + 9) = 2x² - 7x - 3

(iii) 16x⁴ + 8x² + 1

Solution for (iii):

1. Polynomial is in descending order: 16x⁴ + 0x³ + 8x² + 0x + 1

2. Find square root:

___________ 4x² + 0x + 1 | 16x⁴ + 0x³ + 8x² + 0x + 1 16x⁴ --------- 0x³ + 8x² 0x³ + 0x² --------- 8x² + 0x + 1 8x² + 0x + 1 --------- 0

3. Verification: (4x² + 1)² = 16x⁴ + 8x² + 1 ✓

∴ √(16x⁴ + 8x² + 1) = 4x² + 1

(iv) 121x⁴ − 198x³ − 183x² + 216x + 144

Solution for (iv):

1. Polynomial is already in descending order: 121x⁴ − 198x³ − 183x² + 216x + 144

2. Find square root:

_________________ 11x² - 9x - 12 | 121x⁴ - 198x³ - 183x² + 216x + 144 121x⁴ ------------ -198x³ - 183x² -198x³ + 81x² -------------- -264x² + 216x + 144 -264x² + 216x + 144 ------------------- 0

3. Verification: (11x² - 9x - 12)² = 121x⁴ - 198x³ - 183x² + 216x + 144 ✓

∴ √(121x⁴ − 198x³ − 183x² + 216x + 144) = 11x² - 9x - 12

Problem 2: Find 'a' and 'b'

(i) 4x⁴ − 12x³ + 37x² + bx + a is a perfect square

Solution for (i):

1. Assume the square root is of form (2x² + px + q)

2. (2x² + px + q)² = 4x⁴ + 4px³ + (p²+4q)x² + 2pqx + q²

3. Compare coefficients:

- 4p = -12 ⇒ p = -3

- p² + 4q = 37 ⇒ 9 + 4q = 37 ⇒ q = 7

- 2pq = b ⇒ 2(-3)(7) = b ⇒ b = -42

- q² = a ⇒ 49 = a

∴ a = 49, b = -42

(ii) ax⁴ + bx³ + 361x² + 220x + 100 is a perfect square

Solution for (ii):

1. Assume the square root is of form (mx² + px + 10) since √100 = 10

2. (mx² + px + 10)² = m²x⁴ + 2mpx³ + (p²+20m)x² + 20px + 100

3. Compare coefficients:

- 20p = 220 ⇒ p = 11

- p² + 20m = 361 ⇒ 121 + 20m = 361 ⇒ m = 12

- 2mp = b ⇒ 2×12×11 = b ⇒ b = 264

- m² = a ⇒ 144 = a

∴ a = 144, b = 264

Problem 3: Find 'm' and 'n'

(i) 36x⁴ − 60x³ + 61x² − mx + n is a perfect square

Solution for (i):

1. Assume the square root is of form (6x² + px + q)

2. (6x² + px + q)² = 36x⁴ + 12px³ + (p²+12q)x² + 2pqx + q²

3. Compare coefficients:

- 12p = -60 ⇒ p = -5

- p² + 12q = 61 ⇒ 25 + 12q = 61 ⇒ q = 3

- 2pq = -m ⇒ 2(-5)(3) = -m ⇒ m = 30

- q² = n ⇒ 9 = n

∴ m = 30, n = 9

(ii) x⁴ − 8x³ + mx² + nx + 16 is a perfect square

Solution for (ii):

1. Assume the square root is of form (x² + px + 4) since √16 = 4

2. (x² + px + 4)² = x⁴ + 2px³ + (p²+8)x² + 8px + 16

3. Compare coefficients:

- 2p = -8 ⇒ p = -4

- p² + 8 = m ⇒ 16 + 8 = m ⇒ m = 24

- 8p = n ⇒ 8×(-4) = n ⇒ n = -32

∴ m = 24, n = -32

Interactive Practice

Try solving these problems yourself before revealing the solutions!

Remember: (a + b + c)² = a² + b² + c² + 2ab + 2bc + 2ca
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To the most wonderful math teacher/student!