Maths puzzle

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Across
  1. 2. Longest cord of a circle
  2. 4. Name the formula to find the roots of a quadratic equation
  3. 7. "Piece cut off" what does this mean.
  4. 8. "Under root(X2-X1)square+(Y2-Y1)square" what is this formula known as?
  5. 9. A list of numbers in which each term is obtained by adding a fixed number to the preceding term except the first term.
Down
  1. 1. the line drawn from the eye of an observer to the point in the object viewed by the observer.
  2. 3. Each of the numbers in the list is called?
  3. 5. Angle formed by the line of sight with the horizontal line when the point being viewed is above the horizontal level
  4. 6. Area of four walls of a square is known as.