Can someone please explain how to do problems such as...
(4 - 3sqrt7)[2 + 5sqrt7] ?

Question

Can someone please explain how to do problems such as...
(4 - 3sqrt7)[2 + 5sqrt7] ?

andrewkaiser333 · Answer

what is the lesson name and chapter
then i can give you some ways of helping

andrewkaiser333 · Answer

learn it well

andrewkaiser333 · Answer

try this http://www.algebra.com/algebra/homework/Radicals/Radicals.faq.question.271329.html

anonymous · Answer

I'm actually doing math placement review so I don't have an exact name, sorry.

anonymous · Answer

thank you!

andrewkaiser333 · Answer

tat will help you learn it, it is similar to yours

andrewkaiser333 · Answer

that* ok np that shall help

andrewkaiser333 · Answer

tell me if you still do not understand

mathstudent55 · Answer

You are multiplying two numbers.
Each number has a rational part and an irrational part.
Multiply the numbers using FOIL, then combine like terms.

andrewkaiser333 · Answer

here this helps too they just went through one similar using foil. http://openstudy.com/study#/updates/5175f782e4b0be9997e05dd0

anonymous · Answer

this is probably incorrect but is the answer to the example above -97 + 14 sqrt7?

mathstudent55 · Answer

Let me check.

mathstudent55 · Answer

$(4 - 3 \sqrt 7) (2 + 5 \sqrt 7) $

$= 8 + 20 \sqrt 7 - 6 \sqrt 7 - 15 (\sqrt 7)^2 $

$= 8 + 14 \sqrt 7 - 15 \cdot 7 $

$= 8 + 14 \sqrt 7 - 105 $

$= -97 + 14 \sqrt{7} $      This is correct as a final answer

$=14\sqrt 7 - 97$              and so is this


Correct. Good job!

anonymous · Answer

thank you so much!!!

mathstudent55 · Answer

You are very welcome.