Crossword puzzle using mathematical terms

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Across
  1. 4. angle less than 90
  2. 5. a symbol representing an unspecified number that remains invariable throughout a particular series of operations
  3. 8. a mathematical statement that two expressions are equal: it is either an identity in which the variables can assume any value, or a conditional equation in which the variables have only certain values (roots)
Down
  1. 1. a trigonometric function that in a right-angled triangle is the ratio of the length of the hypotenuse to that of the opposite side; the reciprocal of sine
  2. 2. a straight line connecting the centre of a geometric figure, esp a circle or sphere, with two points on the perimeter or surface
  3. 3. the two-dimensional extent of the surface of a solid, or of some part thereof, esp one bounded by a closed curve
  4. 6. the result obtained by adding the numbers or quantities in a set and dividing the total by the number of members in the set
  5. 7. quantity whose cube is a given number or quantity: 2 is the cube root of 8 (usually written 3√ 8 or 81⁄3)