Question 54

If sin(A - B) = $$\frac{1}{2}$$ and cos(A + B) = $$\frac{1}{2}$$ where A > B > 0$$^\circ$$ and A + B is an acute angle, then the value of A is:

Solution

Given,  sin(A - B) = $$\frac{1}{2}$$

$$\Rightarrow$$  sin(A - B) = sin 30$$^{\circ\ }$$

$$\Rightarrow$$  A - B = 30$$^{\circ\ }$$ ........(1)

cos(A + B) = $$\frac{1}{2}$$ and A + B is an acute angle

$$\Rightarrow$$  cos(A + B) = cos 60$$^{\circ\ }$$

$$\Rightarrow$$  A + B = 60$$^{\circ\ }$$ ........(2)

Adding equations (1) and (2),

2A = 90$$^{\circ\ }$$

$$\Rightarrow$$  A = 45$$^{\circ\ }$$

Hence, the correct answer is Option C


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