Question

21) The points A(2,-2), B13,-3), C(4,-4), D(5,-5) all lie in
(a) 2nd Quadrant
(b) 1st Quadrant
c) 4th Quadrant
(d) different quadrants​

Answer 1

An equation involving one or more trigonometrical ratios of unknown angle is called a trigonometric equation e.g. cos2 x – 4 sin x = 1

It is to be noted that a trigonometrical identity is satisfied for every value of the unknown angle where as trigonometric equation is satisfied only for some values (finite or infinite) of unknown angle.

e.g. sec2 x – tan2 x = 1 is a trigonometrical identity as it is satisfied for every value of x Î R.

SOLUTION OF A TRIGONOMETRIC EQUATION

A value of the unknown angle which satisfies the given equation is called a solution of the equation e.g. sin q = ½ Þq = p/6 .

General Solution

Since trigonometrical functions are periodic functions, solutions of trigonometric equations can be generalized with the help of the periodicity of the trigonometrical functions. The solution consisting of all possible solutions of a trigonometric equation is called its general solution.

We use the following formulae for solving the trigonometric equations:

· sin q = 0 Þ q = np,

· cos q = 0 Þq = (2n + 1),

· tan q = 0 Þ q = np,

· sin q = sin a Þq = np + (–1)na, where aÎ [–p/2, p/2]

· cos q = cos aÞq = 2np ± a, where aÎ [ 0, p]

· tan q = tan a Þ q = np + a, where aÎ ( –p/2, p/2)

· sin2 q = sin2 a , cos2 q = cos2 a, tan2q = tan2 aÞq = np±a,

· sin q = 1 Þq = (4n + 1),

· cos q = 1 Þ q = 2np ,

· cos q = –1 Þ q = (2n + 1)p,

· sin q = sin a and cos q = cos aÞ q = 2np + a.

Note:

· Everywhere in this chapter n is taken as an integer, If not stated otherwise.

· The general solution should be given unless the solution is required in a specified interval.

· a is taken as the principal value of the angle. Numerically least angle is called the principal value.

Method for finding principal value

Suppose we have to find the principal value of satisfying the equation sin = – .

Since sin is negative, will be in 3rd or 4th quadrant. We can approach 3rd or 4th quadrant from two directions. If we take anticlockwise direction the numerical value of the angle will be greater than