Solve Triangle Area Equation: Finding X When Area = 2X+16 cm²

Triangle Area with Algebraic Heights

The area of triangle ABC is equal to 2X+16 cm².

Work out the value of X.

333X+5X+5X+5BBBAAACCCDDD

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine the value of X
00:05 Apply the formula for the area of a triangle
00:10 (height(AD) x base(BC)) divided by 2
00:14 Substitute in the relevant values and proceed to solve
00:17 Side BC equals the sum of its parts (BD+DC)
00:28 Multiply by 2 in order to eliminate the denominator
00:37 Isolate AD
00:45 Take out 4 from the parentheses
00:52 We have obtained the height AD
00:55 Apply the Pythagorean theorem to the triangle ADC
01:00 Substitute in the relevant values and proceed to solve
01:10 Isolate X on one side of the equation
01:20 Take the square root
01:25 Subtract 5 and we have obtained X
01:29 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

The area of triangle ABC is equal to 2X+16 cm².

Work out the value of X.

333X+5X+5X+5BBBAAACCCDDD

2

Step-by-step solution

The area of triangle ABC is equal to:

AD×BC2=2x+16 \frac{AD\times BC}{2}=2x+16

As we are given the area of the triangle, we can insert this data into BC in the formula:

AD×(BD+DC)2=2x+16 \frac{AD\times(BD+DC)}{2}=2x+16

AD×(x+5+3)2=2x+16 \frac{AD\times(x+5+3)}{2}=2x+16

AD×(x+8)2=2x+16 \frac{AD\times(x+8)}{2}=2x+16

We then multiply by 2 to eliminate the denominator:

AD×(x+8)=4x+32 AD\times(x+8)=4x+32

Divide by: (x+8) (x+8)

AD=4x+32(x+8) AD=\frac{4x+32}{(x+8)}

We rewrite the numerator of the fraction:

AD=4(x+8)(x+8) AD=\frac{4(x+8)}{(x+8)}

We simplify to X + 8 and obtain the following:

AD=4 AD=4

We now focus on triangle ADC and by use of the Pythagorean theorem we should find X:

AD2+DC2=AC2 AD^2+DC^2=AC^2

Inserting the existing data:

42+(x+5)2=(65)2 4^2+(x+5)^2=(\sqrt{65})^2

16+(x+5)2 =65/16 16+(x+5)^2\text{ }=65/-16

(x+5)2=49/ (x+5)^2=49/\sqrt{}

x+5=49 x+5=\sqrt{49}

x+5=7 x+5=7

x=75=2 x=7-5=2

3

Final Answer

2 cm

Key Points to Remember

Essential concepts to master this topic
  • Formula: Area = base×height2 \frac{base \times height}{2} for any triangle
  • Technique: Factor algebraic expressions like 4(x+8)(x+8)=4 \frac{4(x+8)}{(x+8)} = 4
  • Check: Use Pythagorean theorem to verify: 42+72=(65)2 4^2 + 7^2 = (\sqrt{65})^2

Common Mistakes

Avoid these frequent errors
  • Forgetting to factor the numerator before simplifying fractions
    Don't leave 4x+32x+8 \frac{4x+32}{x+8} unsimplified = missed solution! Students often get stuck with complex fractions when they don't recognize common factors. Always factor the numerator first: 4(x+8)x+8=4 \frac{4(x+8)}{x+8} = 4 .

Practice Quiz

Test your knowledge with interactive questions

Angle A is equal to 30°.
Angle B is equal to 60°.
Angle C is equal to 90°.

Can these angles form a triangle?

FAQ

Everything you need to know about this question

How do I know which side to use as the base and height?

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In this triangle, AD is perpendicular to BC (shown by the right angle symbol), making AD the height and BC the base. Always look for perpendicular lines to identify height!

Why do we need to use the Pythagorean theorem at the end?

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After finding AD = 4, we use the right triangle ADC to find x. Since we know AD = 4, DC = x+5, and AC = 65 \sqrt{65} , Pythagorean theorem helps us solve for x.

What if I get a negative value for x?

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Check your arithmetic! In geometry problems, lengths are always positive. If you get negative values, review your algebraic steps or check if you set up the equation correctly.

Can I solve this without finding AD first?

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No! You need AD (the height) to use the area formula. The key insight is recognizing that the area equation helps you find this missing height value.

How do I verify my final answer x = 2?

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Substitute back: Area = 4×(2+8)2=4×102=20 \frac{4 \times (2+8)}{2} = \frac{4 \times 10}{2} = 20 . Also check: 2x+16=2(2)+16=20 2x + 16 = 2(2) + 16 = 20

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