Given two triangles, if their hypotenuse are congruent, and one pair of their legs are congruent then the two triangles are congruent. In this post, we are going to prove this theorem. In the figure below, ABC and DEF are right triangles with right angles at C and F, respectively. It is given that and . […]

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# Grades 6-8

## Difference of 3-Digit Numbers with Reversed Digits

In the previous post, we proved a theorem that the sum of a 2-digit number with reversed digit is divisible by 11. In this post, we will learn another theorem about numbers with reversed digits. This time, we will explore the difference between two 3-digit numbers with reversed digits. Let’s have the following examples. 231 […]

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## Slope of Perpendicular Lines Theorem

If you have already learned about systems of linear equations, then you have probably discussed that the product of the slope of perpendicular lines is . The proof of this theorem comes from the fact that any point rotated 90 degrees at about the origin becomes . One example of this is shown below. The […]

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