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
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,
In this case, we have (refer to the diagram),
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Learn more about a right - angled triangle here:
brainly.com/question/3770177
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