All of these questions require one thing: trigonometric functions.
There are 3 main trigonometric functions, which can only be used on right triangles: sine, cosine, and tangent.
Sine = opposite / hypotenuse
Cosine = adjacent / hypotenuse
Tangent = opposite / adjacent
When trying to figure out what function to use, we always start by looking from the angle. Take problem a, for example. Looking from angle E, of which the value is not given, we have the side opposite and the side adjacent. Therefore, we should use the tangent function.
---The hypotenuse is always the longest side of the triangle. It is never considered the opposite or adjacent side.
Let's set up our function with the given information from problem a.
tan(x) = 9.7 / 5.2
---The tangent of an unknown angle is equal to the quotient of the opposite side and the adjacent side.
Now, solving for the value of x will require a calculator. We'll need to use what's called an inverse trigonometric function. Most calculators have these directly above the regular trigonometric functions, and the inverse functions are accessed using a "second" key.
---Ensure that your calculator is in degrees, not radians!
x = tan^-1(9.7 / 5.2)
x = 61.805 = 62 degrees
Next, let's take a look at problem b. This time, we're solving for a side length instead of an angle. But, we're still going to start by looking from our angle.
Looking from the 38 degree angle, we are given the adjacent side and an unknown hypotenuse. Therefore, we should use the cosine function.
cosine(38) = 53.1 / r
---The cosine of a 38 degree angle is equal to the quotient of 53.1 and an unknown hypotenuse, r.
Use your algebra skills to isolate the variable r.
r * cosine(38) = 53.1
r = 53.1 / cosine(38)
---From here, all you need to do is plug this into your calculator. Since we are solving for a side length (and given an angle), we are just using the regular trigonometric function buttons on the calculator.
r = 67.385 = 67.4 units
Hope this helps!
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