Right Triangle Side Lengths: Solve for x+9, x+2, and x+10

Pythagorean Theorem with Algebraic Expressions

A right triangle is shown below.

x>1 x>1


Calculate the lengths of the sides of the triangle.

x+9x+9x+9x+2x+2x+2x+10x+10x+10

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:10 Let's find the sides of the triangle.
00:14 Use the Pythagorean theorem to find X in the triangle.
00:22 Apply the shortened multiplication formulas, and open the parentheses.
00:37 Reduce the expression as much as you can.
00:46 Next, group the like terms together.
01:00 Rearrange the equation, so it equals zero on one side.
01:15 Use the quadratic formula to find possible solutions.
01:21 Identify numbers whose sum equals the value B.
01:27 And their product should be equal to the value C.
01:35 These numbers match what we're looking for.
01:41 Substitute these numbers into the quadratic equation.
01:46 Find when each multiplication factor equals zero.
01:52 Work to isolate the unknown value.
01:56 This solution isn't suitable due to the given domain.
02:00 Here is the possible solution for X.
02:04 Substitute this solution into the side expressions to find the sides.
02:10 And that's how we solve the problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

A right triangle is shown below.

x>1 x>1


Calculate the lengths of the sides of the triangle.

x+9x+9x+9x+2x+2x+2x+10x+10x+10

2

Step-by-step solution

To find the lengths of the sides of the right triangle, we will apply the Pythagorean theorem, which states a2+b2=c2a^2 + b^2 = c^2 for a right triangle, where cc is the hypotenuse.

Given the side lengths are x+9x + 9, x+2x + 2, and x+10x + 10, we assume x+10x + 10 is the hypotenuse because it is the largest value and confirm it by checking with the theorem.

Substitute into the Pythagorean theorem:
(x+2)2+(x+9)2=(x+10)2(x + 2)^2 + (x + 9)^2 = (x + 10)^2

Let's expand each side and solve for xx:
(x+2)2=x2+4x+4(x + 2)^2 = x^2 + 4x + 4
(x+9)2=x2+18x+81(x + 9)^2 = x^2 + 18x + 81
(x+10)2=x2+20x+100(x + 10)^2 = x^2 + 20x + 100

Combine these into a single equation:
x2+4x+4+x2+18x+81=x2+20x+100x^2 + 4x + 4 + x^2 + 18x + 81 = x^2 + 20x + 100

Simplify and combine like terms:
2x2+22x+85=x2+20x+1002x^2 + 22x + 85 = x^2 + 20x + 100

Rearrange to form a quadratic equation:
2x2+22x+85x220x100=02x^2 + 22x + 85 - x^2 - 20x - 100 = 0
x2+2x15=0x^2 + 2x - 15 = 0

Factor the quadratic equation:
(x+5)(x3)=0(x + 5)(x - 3) = 0

Solve for xx:
x+5=0x=5x + 5 = 0 \Rightarrow x = -5 (Not valid as x>1x > 1)
x3=0x=3x - 3 = 0 \Rightarrow x = 3

Therefore, substituting x=3x = 3 will provide the side lengths:
<begin><begin> - Short side: x+2=3+2=5x + 2 = 3 + 2 = 5
<sametime><same time> - Other side: x+9=3+9=12x + 9 = 3 + 9 = 12
<sell><sell> - Hypotenuse: x+10=3+10=13x + 10 = 3 + 10 = 13

These side lengths 55, 1212, and 1313 form a well-known Pythagorean triple. Therefore, the solution to the problem is 5,12,135, 12, 13.

3

Final Answer

5,12,13 5,12,13

Key Points to Remember

Essential concepts to master this topic
  • Rule: In right triangles, a2+b2=c2 a^2 + b^2 = c^2 where c is hypotenuse
  • Technique: Expand (x+2)2+(x+9)2=(x+10)2 (x+2)^2 + (x+9)^2 = (x+10)^2 to get quadratic equation
  • Check: Verify 52+122=132 5^2 + 12^2 = 13^2 gives 169 = 169 ✓

Common Mistakes

Avoid these frequent errors
  • Assuming the middle-valued expression is the hypotenuse
    Don't assume x+9 is the hypotenuse just because it's in the middle = wrong equation setup! The hypotenuse must be the longest side, which is x+10 when x > 1. Always identify the largest expression as the hypotenuse first.

Practice Quiz

Test your knowledge with interactive questions

Find the value of the parameter x.

\( (x-5)^2=0 \)

FAQ

Everything you need to know about this question

How do I know which side is the hypotenuse?

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The hypotenuse is always the longest side in a right triangle. Since x > 1, compare x+2, x+9, and x+10. The largest expression x+10 must be the hypotenuse.

What if I get two solutions when factoring?

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Check both solutions against the given constraint! Here we got x = 3 and x = -5, but since x > 1, only x = 3 is valid. Always verify solutions meet the problem conditions.

Do I need to memorize Pythagorean triples?

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No, but recognizing common ones like 3-4-5 and 5-12-13 can help you check your work quickly. The algebra method always works regardless!

Why do we expand the squares instead of taking square roots?

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Taking square roots would give us messy expressions with radicals. Expanding the squares creates a clean quadratic equation that's much easier to solve.

What if my quadratic doesn't factor nicely?

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Use the quadratic formula: x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2-4ac}}{2a} . But most textbook problems are designed to factor cleanly!

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