2 horizontal and parallel lines are intersected by 2 diagonal lines to form a triangle with exterior angles. The top angle of the triangle is (2 x + 10) degrees. The bottom right angle of the triangle is 79 degrees. The exterior angle to the bottom left angle is (6 x + 1) degrees.

What is the value of x?

x = 2.25
x = 11.25
x = 13
x = 22

1 answer

To solve for \( x \) in the given geometry problem, we can use the properties of triangles and exterior angles.

  1. The angles of a triangle sum up to \( 180^\circ \). We know the following angles:
    • Top angle: \( (2x + 10)^\circ \)
    • Bottom right angle: \( 79^\circ \)
    • Let the bottom left angle be \( y \).

Using the triangle angle sum property:

\[ (2x + 10) + 79 + y = 180 \]

This simplifies to:

\[ 2x + y + 89 = 180 \]

Subtract \( 89 \) from both sides:

\[ 2x + y = 91 \tag{1} \]

  1. The exterior angle corresponding to the bottom left angle \( y \) is given as \( (6x + 1)^\circ \). The exterior angle of a triangle is equal to the sum of the two opposite interior angles, which means:

\[ (6x + 1) = (2x + 10) + 79 \]

This can be rearranged to:

\[ (6x + 1) = 2x + 89 \]

Subtracting \( 2x \) from both sides gives:

\[ 6x - 2x + 1 = 89 \]

This simplifies to:

\[ 4x + 1 = 89 \]

Subtracting \( 1 \) from both sides:

\[ 4x = 88 \]

Dividing both sides by \( 4 \):

\[ x = 22 \]

Having solved for \( x \), we can now verify our solution:

  1. If \( x = 22 \):
    • The top angle is \( 2(22) + 10 = 44 + 10 = 54^\circ \).
    • The bottom left angle can be found using \( 2x + y = 91 \):
      • \( 2(22) + y = 91 \) implies \( 44 + y = 91 \), which means \( y = 91 - 44 = 47^\circ \).
    • Now, checking the exterior angle:
      • Bottom left angle \( y = 47^\circ \).
      • The exterior angle to the bottom left angle is \( (6(22) + 1) = 132 + 1 = 133^\circ \).
      • The sum of the interior angles for the triangle:
        • \( 54 + 79 + 47 = 180 \) (which is correct).
      • The exterior angle \( 133^\circ \) is equal to the sum \( 54 + 79 = 133 \) (also correct).

Thus, the value of \( x \) is

\[ \boxed{22} \]