Trigonometry : Similar Triangles

Study concepts, example questions & explanations for Trigonometry

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Example Questions

Example Question #11 : Similar Triangles

Which set of the following triangle dimensions does NOT have the same proportions as a 3-4-5 triangle?

Possible Answers:

\(\displaystyle 6-8-10\)

\(\displaystyle 9-12-15\)

\(\displaystyle \frac{3}{2}-2-\frac{5}{2}\)

\(\displaystyle 1-\frac{4}{3}-\frac{5}{3}\)

\(\displaystyle \frac{1}{3}-\frac{1}{4}-\frac{1}{5}\)

Correct answer:

\(\displaystyle \frac{1}{3}-\frac{1}{4}-\frac{1}{5}\)

Explanation:

In order to determine whether if the dimensions of the triangle are of the same proportions, the ratios of the dimensions must also be the same as the 3-4-5 triangle.

The following scale factors multiplied to the 3-4-5 triangle yield similar proportions.

\(\displaystyle 3(3-4-5)= 9-12-15\)

\(\displaystyle 2(3-4-5)= 6-8-10\)

\(\displaystyle \frac{1}{2}(3-4-5)=\frac{3}{2}-\frac{4}{2}-\frac{5}{2}= \frac{3}{2}-2-\frac{5}{2}\)

\(\displaystyle \frac{1}{3}(3-4-5)=\frac{3}{3}-\frac{4}{3}-\frac{5}{3}= 1-\frac{4}{3}-\frac{5}{3}\)

The only dimensions that cannot be attained by multiplying a particular scale factor with the 3-4-5 is:

\(\displaystyle \frac{1}{3}-\frac{1}{4}-\frac{1}{5}\)

Example Question #281 : Trigonometry

These triangles are similar. Use this to solve for x:

Similar tri 2

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle 12.75\)

\(\displaystyle 20\)

\(\displaystyle 11.25\)

\(\displaystyle 22. \overline{6}\)

Correct answer:

\(\displaystyle 11.25\)

Explanation:

Initially we are given the hypotenuse and one leg of the large triangle, but both legs of the small triangle. To set up a proportion, we need to know both legs of the large triangle, and we can solve for the missing one using the pythagorean theorem:

\(\displaystyle a^2 + b^2 = c^2\), where a and b are the legs and c is the hypotenuse.

\(\displaystyle a^2 + 8^2 = 17^ 2\)

\(\displaystyle a^2 + 64 = 289\) subtract 64 from both sides

\(\displaystyle a^2 = 225\) take the square root of both sides

\(\displaystyle a = 15\)

Now that we have both legs, we can see that 15 corresponds with x, and 8 corresponds with 6, so we can set up a proportion to solve for x:

\(\displaystyle \frac{15}{x} = \frac{8}{6}\)

\(\displaystyle 90 = 8x\) divide both sides by 8

\(\displaystyle 11.25 = x\)

Example Question #291 : Trigonometry

These two triangles are similar. Solve for x:

Similar tri 1

Possible Answers:

\(\displaystyle 20.5\)

\(\displaystyle 10\)

\(\displaystyle 15.625\)

\(\displaystyle 20.8 \overline{3}\)

\(\displaystyle 4.8\)

Correct answer:

\(\displaystyle 10\)

Explanation:

Before we can set up a proportion, we need to know the third side of the larger triangle, since that side is actually the one that corresponds to 6, since both are the shortest sides in their respecitve triangles. We can solve for that side using the Pythagorean Theorem, \(\displaystyle a^2 + b^2 = c^2\)

\(\displaystyle a^2 + 10^2 = 12.5^2\) 

\(\displaystyle a^2 + 100 = 156.25\) subtract 100 from both sides

\(\displaystyle a^2 = 56.25\) take the square root

\(\displaystyle a = 7.5\)

Now we can set up a proportion comparing corresponding sides to solve for x:

\(\displaystyle \frac{7.5}{6 } = \frac{12.5}{x }\) cross-multiply

\(\displaystyle 7.5 x = 75\) divide by 7.5

\(\displaystyle x = 10\)

 

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