Topic 9: Trigonometry – Mathematics Notes Form Two

We can find the trigonometrical ratio of any angle by reading it on a trigonometrial table in the same way as we did in reading logarithm of a number on a logarithimic table.

The angle is read from the extreme left hand column and then the corresponding value under the corresponding column of minutes and seconds whenever there is seconds. If we are given angle with zero minute (0’), we read the corresponding value of an angle under the column labeled 0’.

For example; if we are to find the sin56⁰, we have to go to the column extreme to the left. Run your finger down until you meet56⁰, then slide your finger to the exactly same raw to the column labeled 0’. The answer will is 0.8290.

Another example: find cos 78⁰45′. Read the angle78⁰ to the column extreme to the left and then slide your figure to the exactly same angle until you meet the column labeled 45’. The table I’m using has no 45’, so, I have to read the number near to 45’.

This number is 42’. The answer of cos78⁰42’is 0.1959. the minutes remained, we are going to read them to the difference columns. Slide your figure to the same column of degree78⁰to the difference column labeled 3’ (minutes remained). The answer is 9. But the instructions says, ‘numbers to the difference columns to be subtracted, not added’. This means we have to subtract 9 (0.0009) from 0.1959. When we subtract we remain with 0.1950. Therefore, cos78⁰45’= 0.1950.

Note that, you can read in the same way the tangent of an angle as we read cosine and sine of an angle. Make sure you read the tables of Natural sine or cosine and or tangent and not otherwise.

Problems involving Trigonometric Ratios from Tables

Solve problems involving trigonometric ratios from tables

Example 4