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**Warm Up #3 Find the exact value. 2. –√144 1. √49 ANSWER –12 7 ANSWER**

2. –√144 1. √49 ANSWER 7 ANSWER –12 16 3. Use calculator to approximate the value of to the nearest tenth. 82 ANSWER 2.3

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Homework Check

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x x2 1 2 4 3 9 16 5 25 6 36 7 49 8 64 81 10 100 x x2 11 121 12 144 13 169 14 196 15 225 16 256 17 289 18 324 19 361 20 400

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EXAMPLE 1 Use properties of square roots Simplify the expression. a. 4 81 = 4 81 = 2 9 b. 7 16 = 7 16 = 4 7

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GUIDED PRACTICE GUIDED PRACTICE for Example 1 9 64 3 8 11 25 5 11 = = 15 4 2 15 7 6 36 49 = =

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**Solve a quadratic equation**

EXAMPLE 3 Solve a quadratic equation Solve 3x2 + 5 = 41. 3x2 + 5 = 41 Write original equation. 3x2 = 36 Subtract 5 from each side. x2 = 12 Divide each side by 3. x = + 12 Take square roots of each side. The solutions are and 12 12 –

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**Standardized Test Practice**

EXAMPLE 4 Standardized Test Practice SOLUTION 15 (z + 3)2 = 7 Write original equation. (z + 3)2 = 35 Multiply each side by 5. z + 3 = + 35 Take square roots of each side. z = –3 + 35 Subtract 3 from each side. The solutions are – and –3 – 35 The correct answer is C.

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**Solve a quadratic equation**

EXAMPLE 1 Solve a quadratic equation Solve 2x = –37. 2x = –37 Write original equation. 2x2 = –48 Subtract 11 from each side. x2 = –24 Divide each side by 2. x = + –24 Take square roots of each side. x = + i 24 Write in terms of i. ANSWER The solutions are i and –i

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GUIDED PRACTICE for Example 1 Solve the equation. 2. x2 + 11= 3. 1. x2 = –13. 3. 5x = 3 .

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GUIDED PRACTICE for Example 2 Write the expression as a complex number in standard form. 7. (9 – i) + (–6 + 7i) 8. (3 + 7i) – (8 – 2i) 9. –4 – (1 + i) – (5 + 9i) 9 – i – 6 + 7i 3 + 7i – 8 + 2i –4 – 1 – i – 5 – 9i 3 + 6i -5 + 9i -10 – 10i

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**Multiply complex numbers**

EXAMPLE 4 Multiply complex numbers Write the expression as a complex number in standard form. a. 4i(–6 + i) a. 4i(–6 + i) = –24i + 4i2 Distributive property = –24i + 4(–1) Use i2 = –1. = –24i – 4 Simplify. = –4 – 24i Write in standard form.

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**Multiply complex numbers**

EXAMPLE 4 Multiply complex numbers b. (9 – 2i)(–4 + 7i) = – i + 8i – 14i2 Multiply using FOIL. = – i – 14(–1) Simplify and use i2 = – 1 . = – i + 14 Simplify. = – i Write in standard form.

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**Divide complex numbers**

EXAMPLE 5 Divide complex numbers Write the quotient in standard form. 7 + 5i 1 4i 7 + 5i 1 – 4i = 1 + 4i Multiply numerator and denominator by 1 + 4i, the complex conjugate of 1 – 4i. 7 + 28i + 5i + 20i2 1 + 4i – 4i – 16i2 = Multiply using FOIL. 7 + 33i + 20(–1) 1 – 16(–1) = Simplify and use i2 = 1. – i 17 = Simplify. 13 17 – = + 33 i Write in standard form.

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GUIDED PRACTICE for Examples 3, 4 and 5 Write the expression as a complex number in standard form. 11. i(9 – i) 12. (3 + i)(5 – i) 15 – 3i + 5i – i2 9i – i2 15 + 2i – (-1) 9i – (-1) 15 + 2i + 1 9i + 1 16 + 2i 1 + 9i

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EXAMPLE 6 Plot complex numbers Plot the complex numbers in the same complex plane. a. 3 – 2i b. –2 + 4i c. 3i d. –4 – 3i SOLUTION a. To plot 3 – 2i, start at the origin, move 3 units to the right, and then move 2 units down. b. To plot –2 + 4i, start at the origin, move 2 units to the left, and then move 4 units up. c. To plot 3i, start at the origin and move 3 units up. d. To plot –4 – 3i, start at the origin, move 4 units to the left, and then move 3 units down.

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EXAMPLE 7 Find absolute values of complex numbers Find the absolute value of (a) –4 + 3i and (b) –3i. a. –4 + 3i = (–4)2+32 = 25 5 b. –3i = 02+ (–3)2 = 9 3 0 + (–3i)

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GUIDED PRACTICE for Examples 6 and 7 Find the absolute value of: 15. 4 – i ANSWER 17 16. –3 – 4i ANSWER 5 17. 2 + 5i ANSWER 29 18. –4i ANSWER 4

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**Classwork Assignment:**

WS 4.5 (13-27 odd) and WS 4.6 (1-40 multiples of 3)

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