Posted by **Unknown.** on Tuesday, August 21, 2012 at 9:43am.

Help?

I Kind of understand this , but still I am stuck.

1. (2+4i)/3-i

2. 3√-50 + -72

3.(-4+√-15)^2

4.-4+√-20

5.7√-2(-4√-3)

- Algebra2 - ? -
**Steve**, Tuesday, August 21, 2012 at 10:38am
we kind of don't know where you get stuck. Show us what you got, and we can help you work it the rest of the way.

- Algebra2 -
**Unknown.**, Tuesday, August 21, 2012 at 12:51pm
1. I got 6+3/10

but i don't believe that's the correct answer.

2. i got √21.21+√-8.49

3. i got 34+14√10i

4. i got -1+√5i

- Algebra2 -
**Steve**, Tuesday, August 21, 2012 at 1:10pm
#1: (2+4i)/(3-i)

= (2+4i)(3+i) / (3-i)(3+i)

= (6 + 12i + 2i + 4i^2) / (3^2 - i^2)

= (6 + 14i - 4) / (9+1)

= (2+14i)/10

= 1/5 + 7/5 i

#2: 3√-50 + -72

3√50 i - 72

3*5√2 i - 72

-72 + 15√2 i

in this kind of exercise, there's no call to approximate √ values with decimals. The √ is exact; the decimals are only an approximation.

#3: (-4+√-15)^2

= (-4 + √15 i)^2

= (-4)^2 + 2(-4)(√15 i) + (√15 i)^2

= 16 - 8√15 i - 15

= 1 - 8√15 i

#4: -4+√-20

= -4 + √20 i

= -4 + 2√5 i

#5: 7√-2(-4√-3)

= 7(√2 i)(-4)(√3 i)

= -28 √6 i^2

= 28√6

Does that help? Just take these things step by step, keeping track of the i's and signs.

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