Question 240660: hi,
I am taking a course on N3 maths. Can you help me with the angle of inclination.
The question reads as follows:Determine th slope and angle of inclination of the line passing through points (-2;4) and (4;-1).
To get the andwer calculate m= y2-y1/x2-x1 thus:m=-(5/6)
I know m=tanθ so if the value of m=-5/6 how do i use my calculator to get the degree of the angle? The answer in the book is θ=140.2 degrees?
So how do I get the answer 140.2 degrees????
Found 2 solutions by vleith, jsmallt9:
Answer by vleith(2983)   (Show Source):
You can put this solution on YOUR website! Use your calculator and find the "tan-1" button. Mine is the yellow above TAN (TI-83)
Depends on the calc you have, but you need to find the 'arctan' or 'tan -1'.
Tangent takes degrees and turns them into a ratio.
ArcTan takes a ratio (fraction) and turns it into degrees.
When you plug in tan-1(5/6), you'll get 39.8 degrees. Now you need to know which quadrant the plot it in to find 180-39.8
Answer by jsmallt9(3758) (Show Source):
You can put this solution on YOUR website! (Note: Algebra.com's formula software does not handle exponents on Trig. functions well. So I will use plain text for these and use "^" in front of an exponent and put the exponent in parentheses. For example, for "tan" with an exponent of -1, I will use "tan^(-1)".)
There are many kinds of calculators. They have different sets of keys. And even for the keys that are the same, they may be arranged in different ways. So I am faced with several difficulties as I try to help you learn how to use your calculator. The two biggest issues are:- Angles can be measured in different ways. Degrees and radians are commonly used. Others also exist. Many calculators can work with more than just degrees. Usually you have to set a "mode" which tells the calculator how to treat angles. You can check your current mode by finding the tan(45). If you get 1 for an answer, then your calculator is working with degrees. If you do not get a 1 for tan(45), then you will have to either:
- figure out how to set the mode to degrees; or
- figure what mode you are in and figure out how to convert numbers from that mode into degrees. For example, if your calculator is working in radians, you can multiply a number of radians by
 to convert it to degrees.
- Your problem requires is the ability to calculate the inverse tangent function. There are three ways I know of (and there may be others I do not know of) that calculators provide this function:
- A tan^(-1) key. This is probably the most common.
- Another possibility is that the inverse tangent function requires a sequence of keys: "inv" followed by "tan" follwed by the ratio.
- Probably the least common would be an "arctan" key.
So once you have made sure the calculator is set to use degrees for angles and you have determined what keys to use for the inverse tangent (I am assuming it is tan^(-1) below) just type in
tan^(-1)(-5/6)
If you have trouble getting the right answer, try using
tan^(-1)(-0.83333333333)
-5/6 = -0.83333333333 (the 3's repeat))
If you still do not get the right answer, then your calculator is probably not set to work in degrees. You could try multiplying the answer you do get by and see if that gives you the right answer. If it does, then your calculator is set to work in radians.
If you still cannot get the right answer:- Try a different calculator. For example, most computers have calculator software which you can use. A different calculator may be easier to figure out how to use.
- Find the manual for your calculator and
- Look up "degrees" in the index or table of contents and find out how to set your calculator to use degrees.
- Look up "inverse tangent", "inverse trigonometric functions" or "inverse functions" in the index or table of contents and find out what keys to press and in what order to find the inverse tangent.
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