On the video, the rapper known as 2 Pi reels off rhymes as teenagers in classrooms and hallways sway and bop to the music. It's upbeat. It's catchy. It's . . . math. We solve triangles one by one We ...

For children who find math difficult or frustrating, or who just like to be challenged, there are many cool math games online to play for free. But are they useful? Research shows that the brain’s ...

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