Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Hi,
    can someone tell me where I have gone wrong because I get a square root of negative 15, which is impossible.

    x2+8x-1=0
    x2+8x=1
    (x+4)2=-15
    x+4=square root of -15
    Offline

    0
    ReputationRep:
    (Original post by Louise_1988)
    Hi,
    can someone tell me where I have gone wrong because I get a square root of negative 15, which is impossible.

    x2+8x-1=0
    x2+8x=1
    (x+4)2=-15
    x+4=square root of -15

    x^2+8x-1=0
    (x+4)^2-17=0
    x+4 = +/- square root of 17
    x = - 4 +/- square root of 17.
    Offline

    10
    ReputationRep:
    (Original post by Louise_1988)
    Hi,
    can someone tell me where I have gone wrong because I get a square root of negative 15, which is impossible.

    x2+8x-1=0
    x2+8x=1
    (x+4)2=-15
    x+4=square root of -15
    x^2 + 8x - 1 = 0

    Completing the square: (x + 4)^2

    Multiplying this out: x^2 + 8x + 16 - you need to take away 17 to get -1

    => (x + 4)^2 - 17 = 0
    Offline

    1
    ReputationRep:
    (Original post by Louise_1988)
    Hi,
    can someone tell me where I have gone wrong because I get a square root of negative 15, which is impossible.

    x2+8x-1=0
    x2+8x=1
    (x+4)2=-15
    x+4=square root of -15
    you take 4^2 from the same side, so it becomes -16 - 1 = -17 then move it across.
    Offline

    14
    ReputationRep:
    (Original post by Louise_1988)
    Hi,
    can someone tell me where I have gone wrong because I get a square root of negative 15, which is impossible.

    x2+8x-1=0
    x2+8x=1
    (x+4)2=-15
    x+4=square root of -15
    technically root(-15) isnt impossible but thats a whole other story
 
 
 
Poll
Do you think parents should charge rent?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.