A tricky Algebra from Oxford University Admission Interview. Entrance Aptitude Test. Find x=? & y=?

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  • เผยแพร่เมื่อ 7 พ.ย. 2024

ความคิดเห็น • 28

  • @mrinalkulkarni3151
    @mrinalkulkarni3151 หลายเดือนก่อน +6

    Subtract both given equations a^2-b^2=b-a. i . e (a+b).(a-b)=-1(a-b) i .e a=-1-b . Now substitute this in second equation b^2=-1-b+13. i .e b^2 +b-12=0 i .e (b-4).(b+3)=0 i .e b=(4,-3) now a can be calculated

    • @bobross7473
      @bobross7473 หลายเดือนก่อน

      There are two more solutions. I left a comment about it.

    • @bobross7473
      @bobross7473 หลายเดือนก่อน +1

      Actually you’re right, I forgot he said a =/= b

  • @alessiodaini7907
    @alessiodaini7907 หลายเดือนก่อน +2

    2 cases: a = b, that's possible, since, at this way, the system is composed by 2 identical equations; a ≠ b.
    case a = b:
    a = b => a² = a + 13 => a² - a - 13 = 0 => a = 1/2(1±sqrt(53))
    case a ≠ b
    a² = b + 13 & b² = a + 13
    from this system is true that 13 = a² - b = b² - a, so we have:
    a² - b = b² - a
    a² - b² = b - a = -(a - b)
    a² - b² = (a-b)(a+b), so by substitution:
    (a-b)(a+b) = -(a-b)
    a + b = -1 => a = -(b+1)
    by substituting a in b² = a + 13, we obtain:
    b² = -b + 12 => b² + b - 12 = 0, from that b ={-4,3}
    so if we substitute b solutions in a = -(b+1) there's these couples of solutions:
    (a,b) ={(3,-4),(-4,3)}
    In conclusion we have these solutions, including all cases:
    (a,b) ={(3,-4),(-4,3),(1/2(1±sqrt(53)),1/2(1±sqrt(53)))}
    Yeah, I added also the other cases to find all real solutions

  • @jonathanday6692
    @jonathanday6692 หลายเดือนก่อน

    a^2-13=b, so (a^2-13)^2=a+13.
    Expanding, a^4-26a^2+169=a+13
    Rearrange, giving us a^4-26a^2-a=-156
    Allowing us to get a directly.

  • @unknownguy-x3134
    @unknownguy-x3134 หลายเดือนก่อน +2

    Well if this is oxford then India's 10 grade(high school final year) is way harder

  • @RealQinnMalloryu4
    @RealQinnMalloryu4 หลายเดือนก่อน

    {13ab+13ab ➖ }=26ab^2 2^13ab^2 2^13^1ab^2 2^1^1ab^2 1ab^2 (ab ➖ 2ab+1). {13ba+13ba ➖}=26ba^2 2^13ba^2 2^13^1ba^2 2^1^1ba^2 1ba^2 (ba ➖ 2ba+1).

  • @bobross7473
    @bobross7473 หลายเดือนก่อน

    There are two irrational solutions not shown in the video. The solutions are: (a,b) = (((1+sqrt(53))/2), ((1+sqrt(53))/2)) and (((1-sqrt(53))/2), ((1-sqrt(53))/2)). You can plug these solutions back into the original equations and find that they are indeed valid solutions.

    • @bobross7473
      @bobross7473 หลายเดือนก่อน

      Oh wait sorry you said they aren’t equal, my bad

  • @tameshraj6309
    @tameshraj6309 หลายเดือนก่อน

    a = -3 b =-4

    • @XennialGuy
      @XennialGuy หลายเดือนก่อน

      No, A = +3. If it were -3 then B squared would have to be equal to 10.

  • @doowadiwadi
    @doowadiwadi หลายเดือนก่อน

    Oxford doesn't do admissions like that. Apart from that, the question is way too easy to ever to be considered in case Oxford would do admissions like this.

  • @prollysine
    @prollysine หลายเดือนก่อน

    q=b^2-13 , (b-3)(b^3+3b^2-17b-52)=0 , b=3 , b^3+3b^2-17b-52=0 , (b+4)(b^2-b-13)=0 , b=-4 ,
    b^2-b-13=0 , b=(1+/-V53)/2 ,
    b= 3 , -4 , case 1 , b=3 , a=b^2-13 , a=9-13 , b= -4 , case 2 , b=-4 , a=16-13 , b=3 ,
    solu , (a , b) , (-4 , 3) , (3 , -4) , test , a^2=b+13 , c1 , (-4)^2=3+13 , 16=16 ,
    c2 , 3^2= -4+13 , 9=9 , OK ,

    • @bobross7473
      @bobross7473 หลายเดือนก่อน

      There’s two more solutions

    • @bobross7473
      @bobross7473 หลายเดือนก่อน

      Actually you are right I forgot he said a not equal to b

  • @THIPPESWAMYSAJJANGT
    @THIPPESWAMYSAJJANGT หลายเดือนก่อน +1

    Hi i have another method....

    • @superacademy247
      @superacademy247  หลายเดือนก่อน

      What is it? Share with us!

  • @key_board_x
    @key_board_x หลายเดือนก่อน

    (1): a² = b + 13
    (2): b² = a + 13
    (1) - (2)
    a² - b² = (b + 13) - (a + 13)
    a² - b² = b + 13 - a - 13
    a² - b² = b - a → recall: a² - b² = (a + b).(a - b)
    (a + b).(a - b) = b - a
    (a + b).(a - b) - (b - a) = 0
    (a + b).(a - b) + (a - b) = 0
    (a - b).[(a + b) + 1] = 0 → where: a ≠ b
    a + b + 1 = 0
    a + b = - 1 ← equation (3)
    (1) + (2)
    a² + b² = (b + 13) + (a + 13)
    a² + b² = a + b + 26 → recall (3): a + b = - 1
    a² + b² = 25 ← equation (4)
    From (3):
    a + b = - 1
    (a + b)² = 1
    a² + b² + 2ab = 1 → recall (4): a² + b² = 25
    25 + 2ab = 1
    2ab = - 24 ← equation (5)
    (a - b)² = a² + b² - 2ab → recall (4): a² + b² = 25
    (a - b)² = 25 - 2ab → recall (5): 2ab = - 24
    (a - b)² = 25 + 24
    (a - b)² = 49
    a - b = ± 7 ← equation (6)
    First case:
    a - b = 7 → recall (3): a + b = - 1
    a + b = - 1
    --------------------------the sum
    2a = 6
    → a = 3 → recall: a + b = - 1
    → b = - 4
    Second case:
    a - b = - 7 → recall (3): a + b = - 1
    a + b = - 1
    --------------------------the sum
    2a = - 8
    → a = - 4 → recall: a + b = - 1
    → b = 3

    • @bobross7473
      @bobross7473 หลายเดือนก่อน

      There are two more solutions; see my comment in here

    • @bobross7473
      @bobross7473 หลายเดือนก่อน

      You are right actually, I forgot that he said a not equal to b

  • @XennialGuy
    @XennialGuy หลายเดือนก่อน

    This is part of the entrance exam into Oxford? Are they letting elementary school kids apply these days? Boy is the bar set low.

  • @lto1964
    @lto1964 หลายเดือนก่อน +1

    You are complicating things.

  • @barneynisbet6267
    @barneynisbet6267 หลายเดือนก่อน +1

    More creative to let a=x, b =y. Sketch the two parabolas, verify two solutions (and symmetry). Not hard to realise 13+3 = 4^2 is it? Especially if as claimed, it’s for Oxford interviews. Most Oxford Maths and Physics candidates would do this in their head!

  • @ЭдуардПлоткин-р3л
    @ЭдуардПлоткин-р3л 11 วันที่ผ่านมา

    Неправильное решение.От начала до конца.

  • @XennialGuy
    @XennialGuy หลายเดือนก่อน

    I solved this in my head in less than 2 minutes.
    A = -4
    B = 3
    You made this way too complicated.

  • @mohammadahmadi2980
    @mohammadahmadi2980 หลายเดือนก่อน

    not the only solutions, you can verify

    • @superacademy247
      @superacademy247  หลายเดือนก่อน

      The solutions are restricted. a is NOT equal to b