Trigonometry Tips For Class X SA2 Exam 2015

Some applications of trigonometry and their uses
In this chapter you come across two cases
Case 1:
        

    Here R is point of sight, PQ is object and q is angle of elevation  of  top of PQ.

Case 2:

             

   Here object is at R, and observer is standing at top of PQ i.e., at P and a is angle of depression.

Important point is that a = q (Alternate opposite angles)

KEEP REMEMBER:
• Angle of elevation or depression decreases as the distance between object and observer increases.
• In case you are watching a building from the top of a cliff which is taller than building, then angle of depression of top of building will be smaller than the angle of depression of bottom of building.
• In case you are watching top and bottom of a flag mounted on a building PQ from a point R, then angle of elevation of top of flag will be larger than the angle of elevation of bottom of flag.

Here ,   ф > θ

IMPORTANT ABOUT WORD PROBLEMS IN TRIGONOMETRY

You will face only word problems from this chapter. So, do whatever told in question to form correct trigonometric equations.

For example:

The angle of depression of top and bottom of a 150 m tall light house from a cliff are 30° and 45°. . . .

Check it that here observer is on cliff and watching top and bottom of light house that is 150 m tall . No doubt, cliff will be taller than light house and observer will be at top of cliff. The diagrammatic representation is as follows:

Question is not over at this point.
Then you have to write needful relations in two triangles HFM and LCF.

               (in DFMH)

                     (in DFCL)

Solve these to find the appropriate answer.
Do not try to put the values of    till you reach at last step of your calculation.