Calculate Angle BAD: Quadrilateral with Algebraic Expressions x+3, 2x-2, 5x-2, and 2x+11

Quadrilateral Angles with Algebraic Expressions

Look at the quadrilateral below.

Calculate the size of angle BAD ∢BAD .

AAABBBCCCDDDx+32x-25x-22x+11

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine the size of the angle BAD
00:03 The sum of angles in a quadrilateral equals 360
00:15 Substitute in the relevant values and proceed to solve for X
00:20 Group terms
00:34 Isolate X
00:43 This is the value of X
00:50 Now substitute this X value in the expression for angle BAD and proceed to solve
01:00 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the quadrilateral below.

Calculate the size of angle BAD ∢BAD .

AAABBBCCCDDDx+32x-25x-22x+11

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Set up the equation for the sum of the angles of a quadrilateral.
  • Step 2: Solve for the variable xx.
  • Step 3: Calculate angle BAD \angle BAD using the determined value of xx.

Now, let's work through each step:

Step 1: We know that the sum of the interior angles in a quadrilateral is 360360^\circ. Therefore, we have:

(x+3)+(2x2)+(5x2)+(2x+11)=360 (x + 3) + (2x - 2) + (5x - 2) + (2x + 11) = 360

Step 2: Simplify the equation:

x+3+2x2+5x2+2x+11=360 x + 3 + 2x - 2 + 5x - 2 + 2x + 11 = 360

10x+10=360 10x + 10 = 360

Solve for xx by subtracting 10 from both sides:

10x=350 10x = 350

Divide both sides by 10:

x=35 x = 35

Step 3: Calculate BAD \angle BAD using x=35x = 35:

BAD=x+3=35+3=38 \angle BAD = x + 3 = 35 + 3 = 38^\circ

Therefore, the solution to the problem is 38\mathbf{38^\circ}.

3

Final Answer

38

Key Points to Remember

Essential concepts to master this topic
  • Rule: Sum of interior angles in any quadrilateral equals 360°
  • Technique: Combine like terms: 10x + 10 = 360, so x = 35
  • Check: Verify all angles sum to 360°: 38 + 68 + 173 + 81 = 360° ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting that quadrilateral angles sum to 360°
    Don't assume quadrilateral angles sum to 180° like triangles = wrong x value! This gives completely incorrect angle measures. Always remember quadrilaterals have four angles totaling 360°, not 180°.

Practice Quiz

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Is the straight line in the figure the height of the triangle?

FAQ

Everything you need to know about this question

Why do quadrilateral angles add to 360° instead of 180°?

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A quadrilateral can be divided into two triangles by drawing a diagonal. Since each triangle has angles summing to 180°, the quadrilateral's total is 2 × 180° = 360°.

How do I know which angle expression goes with angle BAD?

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Look at the diagram carefully! The angle at vertex A is labeled with the expression x + 3. Always match the vertex letter to its corresponding angle expression.

What if I get a negative value for x?

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Check your algebra! In this problem, x should be positive (35). Negative x values usually indicate an error in combining like terms or solving the equation.

Can I solve this without setting up the 360° equation?

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No! The angle sum property is essential for finding x. Without it, you have four unknowns and no way to determine their actual values.

How do I verify my final answer is correct?

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Substitute x = 35 into each expression: (35+3) + (2×35-2) + (5×35-2) + (2×35+11) = 38 + 68 + 173 + 81. These should add to 360°!

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