Question

Which triangle’s unknown side length measures 7 units?

Answer 1

7^2 + 5^ 2 = 49 + 25 = 74

The answer is the last picture ( Purple triangle)

Answer 2

For this case we observe that the triangle has an angle of 90 degrees.

We then have to use the Pythagorean theorem to solve the problem.

We have then for the purple triangle:

$x ^ 2 + 5 ^ 2 = (\sqrt{74}) ^ 2$

From here, we can clear the value of x.

We have then:

$x ^ 2 + 25 = 74\\x ^ 2 = 74 - 25\\x ^ 2 = 49$

$x=\sqrt{49}\\x = 7$

Answer:

The triangle whose unknown side is equal to 7 is the triangle number 4.

The purple triangle.