Right Triangle Trig: Finding a Missing Angle

Finding an angle.(Figuring out which ratio to use and getting

to use the 2nd button and one of the trig buttons.)

Ex. 1: Find . Round to four decimal places.

9

17.2

Make sure you are in degree mode (not radians).

9

2.17tan

2nd tan 17.2 9

3789.62

)

Shrink yourself down and stand where the angle is.

Now, figure out which trig ratio you have and set up the problem.

Ex. 2: Find . Round to three decimal places.

23

7

Make sure you are in degree mode (not radians).

23

7cos

2nd cos 7 23

281.72

)

Ex. 3: Find . Round to three decimal places.

400

200

Make sure you are in degree mode (not radians).

400

200sin

2nd sin 200 400

30)

Steps to finding the missing angle of a right triangle using trigonometric ratios:

1. Redraw the figure and mark on it HYP, OPP, ADJ relative to the unknown angle

5.92 kmHYP

OPP

ADJ

2.67 km

Steps to finding the missing angle of a right triangle using trigonometric ratios:

2. For the unknown angle choose the correct trig ratio which can be used to set up an equation

3. Set up the equation

5.92 kmHYP

OPP

ADJ

2.67 km

Steps to finding the missing angle of a right triangle using trigonometric ratios:

4. Solve the equation to find the unknown using the inverse of trigonometric ratio.

5.92 kmHYP

OPP

ADJ

2.67 km

Practice Together:

Find, to one decimal place, the unknown angle in the triangle.

3.1 km2.1 km

YOU DO:

Find, to 1 decimal place, the unknown angle in the given triangle.

7 m

4 m