MAT017
Applied Math II
Procedures
Which Trig Ratio?
Use the trig function definitions:
Sin
=
Side Opposite
===========
Hypotenuse
Cos
=
Side Adjacent
===========
Hypotenuse
Tan
=
Side Opposite
===========
Side Adjacent
Remember that uppercase letters denote angles (C is always the right angle) and lowercase letters
denote sides opposite angles (c is always the hypotenuse).
Therefore, for a particular angle’s functions, the definitions would be:
Sin A =
a/c
Sin B =
b/c
Cos A =
b/c
Cos B =
a/c
Tan A =
a/b
Tan B =
b/a
Where a, b and c are the lengths of the sides opposite angles A, B and C, where angle C is always 90
and side c is always the hypotenuse.
To Find a Side
To find a side, choose a trig function containing an angle and a side that are known and the side that is
unknown. Calculate the trig function with the function key on the calculator. Solve the equation.
Example:
If the length of side a is desired, and side b and Angle B are known, use Tan B.
Tan B =
b/a
Calculate Tan B with the function key on the calculator.
Plug the value into the definition, along with the value for b.
Solve the equation for a.
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MAT017
Applied Math II
Procedures
Which Trig Ratio?
To Find an Angle
To find an angle, choose a trig function containing 2 sides that are known. Calculate the trig function by
dividing the sides. Use the 2nd (shift) key for that function to find the angle.
Example: If angle A is desired and sides a and c are known, choose Sin A.
Sin A =
a/c
Calculate Sin A (a/c) by dividing.
Use the 2nd (shift) SIN A key on the calculator to find SIN-1.
This will be the size of angle A in degrees.
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