Answer:
x = 2
Step-by-step explanation:
<u>Given</u>:
Let A denote the angle of the given triangle which measures ∠A = 81°
Let B denote the angle which measures ∠B = 40°
The length of the side a = x.
The length of the side b = 7 cm.
We need to determine the value of x.
<u>Value of x:</u>
The value of x can be determined using the law of sine formula.
Applying the law of sine, we have;

Substituting the values, we have;

Simplifying, we get;

Cross multiplying, we have;



Thus, the length of the side x is 10.8 cm.
The expression that must be true for a to be parallel to b are mAngle2 = 58Degrees and <1 = 4x - 10
<h3>Lines and angles</h3>
A line is the shortest distance between two points and the point where two lines meet is known as an angle
From the figure shown
m<2 = 58 degrees (alternate exterior angle)
Since the sum of angles on a straight line is 180 degrees, hence;
3x-1+<2 + 4x - 10= 180
3x-1 + 58 + 4x - 10 =180
7x + 47 = 180
7x = 180- 47
7x = 133
x = 19
Hence the expression that must be true for a to be parallel to b are mAngle2 = 58Degrees and <1 = 4x - 10
Learn more on lines and angles here; brainly.com/question/25770607
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