How Do You Write an Indirect Proof?

How Do You Write an Indirect Proof?

Note:

This tutorial looks at using an indirect proof to show that an equilateral triangle cannot have a right angle.

Keywords:

  • problem
  • proof
  • indirect proof
  • equilateral triangle
  • right angle

Background Tutorials

  • Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.

      • What are Acute, Obtuse, Right, and Straight Angles?What are Acute, Obtuse, Right, and Straight Angles?

      What are Acute, Obtuse, Right, and Straight Angles?

      Did you know that there are different kinds of angles? Knowing how to identify these angles is an important part of solving many problems involving angles. Check out this tutorial and learn about the different kinds of angles!

  • Evaluate expressions at specific values of their variables. Include expressions that arise from formulas used in real-world problems. Perform arithmetic operations, including those involving whole-number exponents, in the conventional order when there are no parentheses to specify a particular order (Order of Operations).

      • What is the Substitution Property of Equality?What is the Substitution Property of Equality?

      What is the Substitution Property of Equality?

      If you ever plug a value in for a variable into an expression or equation, you're using the Substitution Property of Equality. This property allows you to substitute quantities for each other into an expression as long as those quantities are equal. Watch this tutorial to learn about this useful property!

  • Solve real-world and mathematical problems by writing and solving equations of the form x + p = q and px = q for cases in which p, q and x are all nonnegative rational numbers.

      • What's the Subtraction Property of Equality?What's the Subtraction Property of Equality?

      What's the Subtraction Property of Equality?

      Solving equations can be tough, especially if you've forgotten or have trouble understanding the tools at your disposal. One of those tools is the subtraction property of equality, and it lets you subtract the same number from both sides of an equation. Watch the video to see it in action!

  • Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles.

      • What is the Triangle Sum Theorem?What is the Triangle Sum Theorem?

      What is the Triangle Sum Theorem?

      When you're dealing with triangles, the Triangle Sum theorem can be very useful in finding interior angle measurements. In this tutorial, learn how to find this helpful theorem!