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Mathematics 13 Online
OpenStudy (anonymous):

(6+6i)/(7+6i)

jimthompson5910 (jim_thompson5910):

Multiply top and bottom by 7-6i

jimthompson5910 (jim_thompson5910):

7-6i is the conjugate of the denominator 7+6i

jimthompson5910 (jim_thompson5910):

So what is (7+6i)(7-6i)

OpenStudy (lifeisadangerousgame):

where are you getting "denominator" from Jim?

OpenStudy (anonymous):

i just need to de divide the two....

jimthompson5910 (jim_thompson5910):

not sure what you mean

OpenStudy (lifeisadangerousgame):

Oh this is divide! I didn't see the divide sign!

OpenStudy (lifeisadangerousgame):

Sorry Jim, you're in the right :P

jimthompson5910 (jim_thompson5910):

So can you tell me what (7+6i)(7-6i) is alisson123?

OpenStudy (lifeisadangerousgame):

She doesn't really understand it yet, this is her first time :/

OpenStudy (anonymous):

no i can't..... i don't know what i;m doing....

OpenStudy (anonymous):

i'm just trying to figure out the answer..... i'm taking a quiz and the teacher is no help

jimthompson5910 (jim_thompson5910):

ok, let's FOIL it out

OpenStudy (anonymous):

foil is for multiplication

jimthompson5910 (jim_thompson5910):

(7+6i)(7-6i) Multiply the First terms: 7*7 = 49 Multiply the Outer terms: 7*(-6i) = -42i Multiply the Inner terms: 6i*(7) = 42i Multiply the Last terms: 6i*(-6i) = -36i^2 = -36(-1) = 36 Now add up all the terms: 49+(-42i)+42i+36 = 85

jimthompson5910 (jim_thompson5910):

So (7+6i)(7-6i) = 85

jimthompson5910 (jim_thompson5910):

Now multiply out (6+6i)(7-6i) (6+6i)(7-6i) = 6*7 + 6*(-6i) + 6i*(7) + 6i*(-6i) (6+6i)(7-6i) = 42 - 36i + 42i - 36i^2 (6+6i)(7-6i) = 42 - 36i + 42i - 36(-1) (6+6i)(7-6i) = 42 - 36i + 42i + 36 (6+6i)(7-6i) = 78 + 6i

jimthompson5910 (jim_thompson5910):

So we go from \[\Large \frac{6+6i}{7+6i}\] to \[\Large \frac{(6+6i)(7-6i)}{(7+6i)(7-6i)}\] to \[\Large \frac{78 + 6i}{85}\] From there, break up the fraction to get \[\Large \frac{78}{85} + \frac{6}{85}i\]

jimthompson5910 (jim_thompson5910):

So in the end, \[\Large \frac{6+6i}{7+6i} = \frac{78}{85} + \frac{6}{85}i\]

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