If $ \cos A + \cos B + \cos C = 0 $ and $ \sin A + \sin B + \sin C = 0 $, then $ \cos(A - B) = $
Show Hint
- 0
- $ \frac{1}{2} $
- $ -\frac{2}{3} $
- $ -\frac{1}{2} $
The Correct Option is D
Solution and Explanation
Step 1: Use the given equations.
$ \cos A + \cos B = -\cos C $
$ \sin A + \sin B = -\sin C $
Step 2: Square and add the equations.
$ (\cos A + \cos B)^2 + (\sin A + \sin B)^2 = (-\cos C)^2 + (-\sin C)^2 $ $ (\cos^2 A + 2 \cos A \cos B + \cos^2 B) + (\sin^2 A + 2 \sin A \sin B + \sin^2 B) = \cos^2 C + \sin^2 C $
Step 3: Simplify using trigonometric identities.
$ (\cos^2 A + \sin^2 A) + (\cos^2 B + \sin^2 B) + 2 (\cos A \cos B + \sin A \sin B) = 1 $
$ 1 + 1 + 2 \cos(A - B) = 1 $
Step 4: Solve for $ \cos(A - B) $.
$ 2 + 2 \cos(A - B) = 1 $
$ 2 \cos(A - B) = -1 $
$ \cos(A - B) = -\frac{1}{2} $
Step 5: Conclusion.
The value of $ \cos(A - B) $ is $ -\frac{1}{2} $.
Top AP EAPCET Mathematics Questions
- $D = \left\{x\in\mathbb{R}: f\left(x\right) =\sqrt{\frac{x - \left|x\right|}{x - \left[x\right]}} \text{is defined} \right\}$ and $C$ be the range of the real function $g(x) = \frac{2x}{4 + x^{2}}$. Then $D \cap C$
- $f\left(x\right) = \frac{x}{e^{x}-1} + \frac{x}{2} + 2 \cos^{3} \frac{x}{2} $ on $R-\left\{0\right\} $ is
- Consider the following lists.
List-I List-II (A) $f(x) = \frac{|x+2|}{x+2} , x \ne -2 $ (I) $[\frac{1}{3} , 1 ]$ (B) $(x)=|[x]|,x \in [R$ (II) Z (C) $h(x) = |x - [x]| , x \in [R$ (III) W (D) $f(x) = \frac{1}{2 - \sin 3x} , x \in [R$ (IV) [0, 1) (V) { -1, 1} - If $[x]$ is the greatest integer less than or equal to $x$ and $|x|$ is the modulus of $x$. then the system of three equations $2x + 3 | y | + 5[z] = 0, x + |y| - 2[z] = 4, x + |y| + |z| = 1$ has
- Investigate the values of $\lambda$ and $\mu$ for the system $x+2 y+3 z=6, x+3 y+5 z=9$, $2 x+5 y+\lambda z=\mu$ and match the values in List - I with the items in List - II.
List I List II (A) $\lambda=8, \mu \neq 15$ 1. Infinitely many solutions (B) $\lambda \neq 8, \mu \in R$ 2. No solution (C) $\lambda=8, \mu=15$ 3. Unique solution
Top AP EAPCET Trigonometric Identities Questions
If \(\cos \alpha + \cos \beta + \cos \gamma = \sin \alpha + \sin \beta + \sin \gamma = 0,\) then evaluate \((\cos^3 \alpha + \cos^3 \beta + \cos^3 \gamma)^2 + (\sin^3 \alpha + \sin^3 \beta + \sin^3 \gamma)^2 =\)
- If \[ \cos \frac{ \pi }{8} + \cos \frac{3 \pi }{8} + \cos \frac{5 \pi }{8} + \cos \frac{7 \pi }{8} = k, \] then evaluate \[ \sin^{-1} \left( \frac{k}{\sqrt{2}} \right) + \cos^{-1} \left( \frac{k}{3} \right)= \]
- Evaluate the expression: \[ \frac{\cos 10^\circ + \cos 80^\circ}{\sin 80^\circ - \sin 10^\circ}. \]
- Evaluate the expression: \[ \frac{\sin 1^\circ + \sin 2^\circ + \dots + \sin 89^\circ}{2(\cos 1^\circ + \cos 2^\circ + \dots + \cos 44^\circ) + 1} =\]
- The number of ordered pairs \( (x, y) \) satisfying the equations: \[ \sin x + \sin y = \sin (x + y) \quad \text{and} \quad |x| + |y| = 1. \]
Top AP EAPCET Questions
- A body is projected from the ground at an angle of $\tan^{-1} \left( \frac{8}{7}\right)$ with the horizontal. The ratio of the maximum height attained by it to its range is
- The four quantum numbers of the valence electron of potassium are :
- A lens forms real and virtual images of an object, when the object is at $u_{1}$ and $u_{2}$ distances respectively. If the size of the virtual image is double that of the real image, then the focal length of the lens is (take, the magnification of the real image as $m$ )
- Two spheres $P$ and $Q$, each of mass $200\, g$ are attached to a string of length one metre as shown in the figure. The string and the spheres are then whirled in a horizontal circle about $O$ at a constant angular speed. The ratio of the tension in the string between $P$ and $Q$ to that of between $P$ and $O$ is $(P$ is at mid-point of the line joining $O$ and $Q$ )
- The volume of $0.02\, M$ acidified permanganate solution required for complete reaction of $60\, mL$ of $0.01\, MI^{-}$ ion solution to form $I_2$ in $mL$ is