1. The SDN iPhone App is back and free through November! Get it today and please post a review on the App Store!
    Dismiss Notice
  2. Dismiss Notice
  3. Guest, be sure to check out How To Get Into Dental School, our free downloadable PDF with step-by-step details for dental school applicants!
    Dismiss Notice
  4. Dismiss Notice
Dismiss Notice

Interview Feedback: Visit Interview Feedback to view and submit interview information.

Interviewing Masterclass: Free masterclass on interviewing from SDN and Medical College of Georgia

Need some help on QR

Discussion in 'DAT Discussions' started by gameguard, Jul 27, 2006.

  1. gameguard

    gameguard Junior Member
    5+ Year Member

    Joined:
    Jun 19, 2006
    Messages:
    23
    Likes Received:
    0
    Well, I was always pretty good at math and didnt think it to be much of a problem. However, ive been doing the topscore problems and some of the questions they give are not very "standard math" ... at least in my book.

    There was numerous problems involving very random equations (given in the solutions). For example, there was a question with 3 coordiantes and I was supose to find the area of the triangle - which was not any special triangle. the eq. they gave was :
    A = 1/2[(x1y2 + x2y3 + x3y1) - (y1x2 + y2x3 + y3x1)]

    I duno about you guys but I have never in my life come across this equation. Im guessing its some variation of herons formula and distance formula...

    I mean I could use distance formula for each side and then plug it in to herons formula, but that would be VERY messy and time consuming. This is just an example of the kind of things that caught me off guard. There was alot of questions that sported unorthodox equations in their solutions (eqs that wernt covered in kaplan and are even hard to come by on the net)

    I guess im rambling... what im trying to get at is this. For those of you who took the test, how many times did you come across a question that required you to know some kind of special formula to solve in any reasonable amount of time?

    Also, if you guys could add some equations that you found useful I would really appreciate it.

    Thank you~
     
  2. Note: SDN Members do not see this ad.

  3. gameguard

    gameguard Junior Member
    5+ Year Member

    Joined:
    Jun 19, 2006
    Messages:
    23
    Likes Received:
    0
  4. wclubin

    wclubin Member
    7+ Year Member

    Joined:
    Jun 13, 2003
    Messages:
    54
    Likes Received:
    0

    Well the above equation clearly comes from the standard formula for the equation of a triangle namely Area equals 1/2 the base times the altitude. Both the base and the altitude used the distance formula and so that is why there are no square root signs left. when you mult a square root by another square root the square roots go away. And so there for you are left with !/2(stuff)(stuff). after squaring everthing out in the inside and bringing all neg terms to one side and factoring out the negative sign you arive at what you get above. It is just the standard formula with some algebraic manipulation. no new formulas. I would have to see the specific question to answer more specificly.
     
  5. gameguard

    gameguard Junior Member
    5+ Year Member

    Joined:
    Jun 19, 2006
    Messages:
    23
    Likes Received:
    0
    uhh... well the question is :

    In a two dimensional coordinate system, point A=(3,-6), point B=(1,1) and point C=(7,6). Find the area of the triangle ABC.

    Answer is 26



    I still cant seem to come up with the formula given ... This triangle is not any kind of standard triangle (at least i dont think) so .5bh seems pretty complicated.


    also any aditional help regarding my rant up there would be appreciated :0
     
  6. sonysonysony

    2+ Year Member

    Joined:
    Jun 12, 2006
    Messages:
    23
    Likes Received:
    0
    Status:
    Pre-Dental
    Whenever you have a (x, y) point system for the 3 points of the triangle, you will need to find the distance between each of the two points. To find the distance b/w the points (x1, y1) and the points (x2, y2), this equation must be used.

    (d)square=(x1-x2)square+(y1-y2)square

    I think they just combined this equation with 1/2bh to get the equation in that book.

    Hope this helps.

    later


     
  7. DMD to Be

    DMD to Be not luffin' this weather.
    5+ Year Member

    Joined:
    Mar 22, 2006
    Messages:
    387
    Likes Received:
    0
    Status:
    Pre-Dental
    There must be an easier way to work this problem...Besides, you have less than a minute to do it...no time to do 3 distance formulas and the 1/2 bh...
     
  8. gameguard

    gameguard Junior Member
    5+ Year Member

    Joined:
    Jun 19, 2006
    Messages:
    23
    Likes Received:
    0
    really... and how can you find the height when its not a right triangle and there are no angles.
     
  9. luder98

    luder98 Senior Member
    5+ Year Member

    Joined:
    Sep 17, 2004
    Messages:
    652
    Likes Received:
    0
    Status:
    Dentist
    I saw a question similar but easier on my DAT. The one I had was a special case when two points are on one horizontal line. Here is how I did it:
    - Draw a small xOy plane
    - Put all the three points into the plane
    You can quickly find one base based on the two points on the same horizontal line (== the absolute value of the difference between the x-values). The height is the absolute value of the difference between the third y-value with the y-value of the other two. Then use 1/2bh formula.
    You can use this method in similar manner if two of the three points are on one vertical line.
    For your question, the quickest way (if you don't remember the formula) is to find one base from two points. Find the equation pass through these two points. Find the distance from the third point to this equation. Then use 1/2bh formula. If you can do all that in less than 1 min, then do it. Otherwise, just mark and move one. There are many more much less calculating questions later on. You don't want to miss those. Good Luck!
     
  10. gameguard

    gameguard Junior Member
    5+ Year Member

    Joined:
    Jun 19, 2006
    Messages:
    23
    Likes Received:
    0

    yea, i got ya. Thanks for the reply~
     
  11. tom_servo_dds

    tom_servo_dds Senior Member
    2+ Year Member

    Joined:
    Jun 20, 2006
    Messages:
    244
    Likes Received:
    0
    Status:
    Pre-Dental
    1/2bh should work for all triangles, regardless of if they are right triangles.
     
  12. DrJimLa

    DrJimLa New Member

    Joined:
    Aug 3, 2006
    Messages:
    4
    Likes Received:
    0
    Status:
    Pre-Dental
    was very interested by the ? bc i saw one similiar on my practice test....
    if you have three coordinates and one is the origin (or you can move all points to make one the origin the equation is fairly easy)
    so for your example
    A (1,1)-------------becomes (0,0)
    B (3,-6)-----------------------(2,-7)
    C (7,6)------------------------(6,5)
    then use the equations
    Area= 1/2 [(Bx*Cy)-(By*Cx)] and those are absolute value brackets
    Area= 1/2 [2*5-(-7*6)]
    A= 1/2 [10+42]= 1/2 [52]
    A=26
    hope thats is useful and it shows up on DAT for someone! :thumbup:
     
  13. tom_servo_dds

    tom_servo_dds Senior Member
    2+ Year Member

    Joined:
    Jun 20, 2006
    Messages:
    244
    Likes Received:
    0
    Status:
    Pre-Dental
    Great help, thanks!
     
  14. dental#1

    dental#1 Fla DDS
    2+ Year Member

    Joined:
    Jul 22, 2006
    Messages:
    62
    Likes Received:
    0
    Status:
    Pre-Dental
    This problem is on Topscore and my answer was real one I think,so let me know!I think You need to carry the negative sign. I am meeting with a tutor today so I will be able to see if there is an easier way

    (X1Y2 + X2Y3 + X3Y1) - (Y1X2 + Y2X3 + Y3X1)

    (3*1 + 1*6 + 7*-6) - ( -6*1 + 1*7 + 6*3)

    (3*1 + 1*6 + 7*-6) - ( 6*1 - 1*7 - 6*3)

    3+6+ (-42) + 6 -7 -18

    -33-19= -52 1/2 = 26
     

Share This Page