Math Problem Statement

Multiply the following complex numbers. ( − 3 + 7 i ) ⋅ ( 2 + 5 i )

Solution

To multiply two complex numbers, you use the distributive property (FOIL method for binomials). Let's multiply the complex numbers (3+7i)(-3 + 7i) and (2+5i)(2 + 5i).

(3+7i)(2+5i)(-3 + 7i) \cdot (2 + 5i)

Step 1: Apply the distributive property (FOIL)

(3)2+(3)5i+(7i)2+(7i)5i(-3) \cdot 2 + (-3) \cdot 5i + (7i) \cdot 2 + (7i) \cdot 5i

Step 2: Perform the multiplication

=615i+14i+35i2= -6 - 15i + 14i + 35i^2

Step 3: Simplify the result

We know that i2=1i^2 = -1, so:

35i2=35(1)=3535i^2 = 35(-1) = -35

Now, combine like terms:

6+(35)=41-6 + (-35) = -41 15i+14i=i-15i + 14i = -i

Final Answer:

41i-41 - i

So, the product of (3+7i)(-3 + 7i) and (2+5i)(2 + 5i) is 41i-41 - i.

Would you like further clarification or details on any step?


Here are 5 related questions to explore:

  1. How do you divide two complex numbers?
  2. What is the magnitude of a complex number?
  3. What is the conjugate of a complex number, and how is it used in division?
  4. How do you convert a complex number into polar form?
  5. What is the real and imaginary part of a complex number?

Tip: When multiplying complex numbers, always remember to use i2=1i^2 = -1 to simplify terms!

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Multiplication of Complex Numbers
Distributive Property
Imaginary Numbers

Formulas

(a + bi)(c + di) = ac + adi + bci + bdi^2
i^2 = -1

Theorems

Distributive Property
Properties of i (imaginary unit)

Suitable Grade Level

Grades 9-11