SOLUTION: A rectangles length is 3 times as long as its width. The diagonal of the rectangle is 10cm. Use Pythagoras theorem to solve. This is what I have tried, but it does not seem to

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Question 945793: A rectangles length is 3 times as long as its width. The diagonal of the rectangle is 10cm. Use Pythagoras theorem to solve.
This is what I have tried, but it does not seem to work:
I use this formula: a^2=b^2+c^2
10^2=3x^2+x^2
100=4x^2
100/4=4x^2/4
25=x^2
sqrt( 25 )=sqrt( x^2 )
5=x
x cannot equal 5. I don't know what I am doing wrong.

Answer by 428225(90) About Me  (Show Source):
You can put this solution on YOUR website!

You need to make a habit of using brackets. You were right in recognizing that the length was 3x. Since 3x=a, so when you find a^2, you have to square the whole of 3x. However you thought it was 3%28x%29%5E2, when it was actually %283x%29%5E2. So if you had used brackets you probably would have gotten the right answer.