Homework Help: Algebra

Posted by Breanna on Monday, June 22, 2009 at 10:40pm.

Simplify: Write answers in the form of a + bi, where a and b are real numbers.

a. (1-2i)(1+3i)

b. (3-5i)(8-2i)

Algebra - bobpursley, Monday, June 22, 2009 at 10:59pm
Use FOIL to multiply them out.
Algebra - Breanna, Monday, June 22, 2009 at 11:15pm
IS this correct, i notice that i^2 = -1 what does this mean?

(1-2i)(1+3i)
=1+3i-2i-6i^2
=1+ i-6i^2
= 1+i-6i
Algebra - bobpursley, Monday, June 22, 2009 at 11:51pm
no, 6i^2 is 6*(-1)
so the last term is +6 and the final answer is
7+i
Algebra - Breanna, Tuesday, June 23, 2009 at 12:11am
So did I do any of this correct? What do I need to fix?
Algebra - MathMate, Tuesday, June 23, 2009 at 12:56am
You have basically done it correctly, but omitted to change the sign of the last term because i²=-1

(1-2i)(1+3i)
=1+3i-2i-6i^2
=1+ i-6i^2
= 1+i +6i
Algebra - MathMate, Tuesday, June 23, 2009 at 12:57am
Oops, it should read:

(1-2i)(1+3i)
=1+3i-2i-6i^2
=1+ i-6i^2
= 1+i +6
=7+i

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