Results 1 to 6 of 6

Math Help - Area of triangle

  1. #1
    Member
    Joined
    Nov 2009
    Posts
    78

    Question Area of triangle

    In the attached figure, ST=5cm & QR=9cm. The area of the larger triangle is 50 sq.cm. What is the area of the black region?

    Thanks,

    Ron
    Attached Thumbnails Attached Thumbnails Area of triangle-triangle.gif  
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,830
    Thanks
    123
    Quote Originally Posted by rn5a View Post
    In the attached figure, ST=5cm & QR=9cm. The area of the larger triangle is 50 sq.cm. What is the area of the black region?

    Thanks,

    Ron
    The shaded region is:

    (area of the large triangle) - (area of triangle QRS)

    The area of a triangle is calculated by:

    a_{\Delta} = \frac12 \cdot base \cdot height

    with \overline{QR} = base and \overline{ST} = height
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member
    Joined
    Jul 2009
    From
    Melbourne
    Posts
    274
    Thanks
    4
    The problem is how to find the height of the whole triangle..
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,830
    Thanks
    123
    Quote Originally Posted by rn5a View Post
    ... The area of the larger triangle is 50 sq.cm. What is the area of the black region?

    ...
    Quote Originally Posted by jgv115 View Post
    The problem is how to find the height of the whole triangle..
    Honestly I don't understand why you want to know the height of the triangle QRP because you already know that the area of the this triangle is 50 cm².

    But: Since you know that \overline{QR} = 9\ cm you can use the value of the area and the length of the base to calculate the length of the height:

    50 =\frac12 \cdot 9 \cdot h~\implies~ h= \frac{100}9

    And now?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Senior Member
    Joined
    Jul 2009
    From
    Melbourne
    Posts
    274
    Thanks
    4
    I should learn to read.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Dec 2009
    Posts
    2
    I thought you just subtract the area of the smaller traingle from the triangle of the whole to get 27.5 sq.cm?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Area of a triangle
    Posted in the Geometry Forum
    Replies: 4
    Last Post: April 27th 2010, 10:29 AM
  2. Replies: 1
    Last Post: October 28th 2008, 07:02 PM
  3. Replies: 7
    Last Post: July 19th 2008, 06:53 AM
  4. The area of a triangle within a triangle
    Posted in the Geometry Forum
    Replies: 4
    Last Post: April 28th 2008, 03:27 AM
  5. Replies: 27
    Last Post: April 27th 2008, 10:36 AM

Search Tags


/mathhelpforum @mathhelpforum