Math Problem Statement

Draw a right-angled triangle containing an angle of 45°. If one of the shorter sides has length one, write down the lengths of the other sides without using trigonometry. Hence find the exact values of sin 45°, cos 45° and tan 45°.

Solution

To solve this problem, we start by drawing a right-angled triangle with one angle of 45°. In a right-angled triangle, the two non-right angles must sum to 90°. Therefore, if one of these angles is 45°, the other must also be 45°. This makes the triangle an isosceles right-angled triangle, where the two legs are of equal length.

Given that one of the shorter sides (one leg of the triangle) has a length of 1, we can determine the lengths of the other sides as follows:

  1. Both legs are equal in length: Since the triangle is isosceles and one leg is 1, the other leg is also 1.

  2. Hypotenuse calculation: The length of the hypotenuse (let's denote it as cc) can be found using the Pythagorean theorem, which states:

    c2=a2+b2c^2 = a^2 + b^2

    Substituting the known lengths:

    c2=12+12=1+1=2c^2 = 1^2 + 1^2 = 1 + 1 = 2

    Thus, c=2c = \sqrt{2}.

Now, we can find the exact values of the trigonometric functions for the 45° angle:

  1. sin45\sin 45^\circ: sin45=oppositehypotenuse=12\sin 45^\circ = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{1}{\sqrt{2}}

  2. cos45\cos 45^\circ: cos45=adjacenthypotenuse=12\cos 45^\circ = \frac{\text{adjacent}}{\text{hypotenuse}} = \frac{1}{\sqrt{2}}

  3. tan45\tan 45^\circ: tan45=oppositeadjacent=11=1\tan 45^\circ = \frac{\text{opposite}}{\text{adjacent}} = \frac{1}{1} = 1

For exact values, we often rationalize the denominators:

  • sin45=12=22\sin 45^\circ = \frac{1}{\sqrt{2}} = \frac{\sqrt{2}}{2}
  • cos45=12=22\cos 45^\circ = \frac{1}{\sqrt{2}} = \frac{\sqrt{2}}{2}
  • tan45=1\tan 45^\circ = 1

Thus, the exact values are:

  • sin45=22\sin 45^\circ = \frac{\sqrt{2}}{2}
  • cos45=22\cos 45^\circ = \frac{\sqrt{2}}{2}
  • tan45=1\tan 45^\circ = 1

Would you like any further explanation or have any questions about these results?

Here are 5 questions you might consider asking next:

  1. How can we use trigonometry to find the area of the triangle?
  2. What are the properties of isosceles right-angled triangles?
  3. Can you explain why the sine and cosine of 45° are equal?
  4. How do you rationalize a fraction with a square root in the denominator?
  5. What are some real-life applications of right-angled triangles?

Tip: In trigonometry, rationalizing denominators is often done to simplify expressions, making them easier to work with or recognize.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Right-angled triangles
Isosceles triangles

Formulas

Pythagorean theorem

Theorems

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Suitable Grade Level

Grades 9-12