Possible Clues:

• Mathematical function for English in 1 situation
• Straight line through a circle
• Line intersecting a curve
• Line of ascent that's fixed
• The line intersects a curve more than once
• Put energy into inadequate triangular relationship
• Curve-cutting line
• Line that intersects a circle in two places
• Ratio of the hypotenuse to the adjacent side in a right-angled triangle
• Mathematician's line is able to divide group