The correct answer is, b=4.
Given Information and To Find
It is given that in a right angled-triangle lmn,
∠m = 90°
∠l = x°
ln = 20 units
lm = 3b units
[tex]secx = \frac{5}{3}[/tex]
We have to find the value of b.
What is a right-angled triangle?
A right triangle is a triangle in which one of the angles is at a right angle or two of the sides are perpendicular, or more formally, an orthogonal triangle, formerly known as a right-angled triangle. Trigonometry's fundamental concept is the relationship between a right triangle's sides and other angles.
Applying Trigonometry
We know that in a right angled-triangle,
[tex]sec x=\frac{hypotenuse}{base}[/tex]
In this case, we have (refer to the diagram),
[tex]secx=\frac{ln}{lm}[/tex]
⇒ [tex]\frac{20}{3b} = \frac{5}{3}[/tex]
⇒ [tex]20(3) = 3b(5)[/tex]
⇒ [tex]15b = 60[/tex]
⇒ [tex]b=4[/tex]
Learn more about a right - angled triangle here:
https://brainly.com/question/3770177
#SPJ4
