Drag numbers to form pairs that add up to the same sum.
Tap to connect the visual pairs to the math.
Tap a block above that represents
Tap the box to select the formula for the number of pairs.
Formula constructed!
We know . Slide to substitute it in.
Slide right to simplify Formula derived!
Use the formula to evaluate the series.
You've explored the intuition, built the formulas, and solved the sums.