Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Please help me with these questions

  1. May 20, 2008 #1
    Please help me with these questions!!

    1. Factorize:
    a) 7(x+y)² + 48(x+y) - 7
    b) 5 - 20x²
    c) 2xy² - 22xy + 48x




    I tried a lot to solve these equations, can't work it out!! Here are some of the solutions i got!! for (a):
    =7(x²+2xy+y²) + 48 (x+y) - 7
    =7x²+14xy+7y²+48x+48y - 7
    (cant work it out any further)


    for (b):

    (√5)² - (2√5)²
    (√5+2√5) (√5+2√5) (is it correct??!!)

    i cant even think of away to work out the third one!!!

    ( i know this is maths but pls help me out!!)
     
  2. jcsd
  3. May 20, 2008 #2

    symbolipoint

    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    You went way into the wrong direction for 1a. FACTORIZE! I would first recognize the variable as (x+y), and then you just try to deconstruct the trinomial into its two binomial factors.
     
  4. May 20, 2008 #3
    For 1(a) put (x+y) = u

    7u2 + 48u - 7

    now solve for u.

    (b) 5 - 20x2

    can you take out a factor which is common to both 5 and 20?
     
  5. May 20, 2008 #4

    symbolipoint

    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    Regarding what Kushal and I said, one would usually begin breaking the expression into the incomplete:

    (7u )(u ) having summands either -1 and 7 or 1 and -7 or -7 and 1 or 7 and -1;
    but none of those are helpful. We would not use completion of square unless we were solving an equation, which we not have; we HAVE just the expression 7u^2 +48u - 7.
     
  6. May 20, 2008 #5

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    And for (c), first find all common factors in the terms.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook