If sine of x degrees equals four-fifths, what is the value of b?

triangle LMN in which angle M measures 90 degrees, angle L measures x degrees, LN measures 22.5 units, and NM measures 3b units

b = 4
b = 5
b = 6
b = 7

1 answer

In triangle LMN, we know the following:

  • Angle M is a right angle (90 degrees).
  • Angle L measures \( x \) degrees.
  • The side \( LN \) (the hypotenuse) measures 22.5 units.
  • The side \( NM \) (an opposite side to angle L) measures \( 3b \) units.

Given that \( \sin(x) = \frac{4}{5} \), we can use this information to set up the sine definition for angle L:

\[ \sin(L) = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{NM}{LN} \]

Substituting the lengths we have:

\[ \sin(x) = \frac{3b}{22.5} \]

Now, plugging in the value of \( \sin(x) \):

\[ \frac{4}{5} = \frac{3b}{22.5} \]

To solve for \( b \), we can cross-multiply:

\[ 4 \cdot 22.5 = 3b \cdot 5 \] \[ 90 = 15b \]

Now, isolate \( b \):

\[ b = \frac{90}{15} = 6 \]

Thus, the value of \( b \) is:

\[ \boxed{6} \]