Give the exact value of each expression?

Question

4. tan 13π/12
5. cos18°cos192°-sin18°sin192°
6. sin 13π/12 cos 15π/12+cos 13π/12 sin 15π/12
7. cos 22π/15 cos 47π/15+sin 22π/15 sin 47π/15

Answer 1

4) The expression

-----> (1)

From trigonometric table

And The value of

 

Substitute the above values in equation (1).

Answer 2

5)The expression

Compare it to trigonometric formula

In third quadrant 'cos' is negitive.

From trigonometric table

.

Answer 3

6) The expression

Compare it to trigonometric formula

In first quadrant 'sin' is positive.

From trigonometric table

Answer 4

7) The expression is

Compare it to trigonometric formula 

cos(-x ) = cos(x)

In fourth quadrant 'cos' is positive.

From trigonometric table

.