Equal Triangle Algebra

Geometry Level 2

The above right triangles have the same area and height h h . Choose all the correct options given.

Select one or more

x = 5 x=5 y = 2 y=2 y = 5 y=5 x = 4 x=4

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3 solutions

As the areas are same........................................ 1/2×(x+1)×h =1/2×5×h On solving we get x=4. As base of both the triangles are same, the hypotenuese of both triangles will be equal...... Therefore, (x+y)=(2y+2) Substitute x=4 and on simplification we get y=2.

That's exactly the solution pathway intended for this problem. Also, it is meant to be done with two equations as we have two unknowns. Great job!

Michael B Staff - 4 years, 10 months ago
Michael B Staff
Jul 25, 2016

If these triangles are in fact equal, then we can assume the bases and hypotenuses are equal to each other.

First find x x by setting the bases equal to each other. Subtract 4 from each side. x + 1 = 5 x = 4 \begin{aligned} x+1&=5\\ x=4\\ \end{aligned} Then use your result from x x to solve for y y and set the hypotenuses equal to each other. Solve for y y by subtracting y y and 2 from each side. 4 + y = 2 y + 2 4 = y + 2 2 = y \begin{aligned} 4+y&=2y+2\\ 4&=y+2\\ 2&=y\\ \end{aligned}

Since the areas are equal, we have

1 2 ( h ) ( x + 1 ) = 1 2 ( h ) ( 5 ) \dfrac{1}{2}(h)(x+1) = \dfrac{1}{2}(h)(5)

x + 1 = 5 x+1=5

x = 4 x=4

We observed that the bases are also equal, so the triangles are congruent. So

x + y = 2 y + 2 x+y = 2y+2

4 + y = 2 y + 2 4+y=2y+2

4 2 = 2 y y 4-2=2y-y

2 = y 2 = y

Note: In my solution, I assumed that the bases are not equal. But if we look further, we can see that the bases are equal.

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