Download App

PART - 1 CH - 3 Trigonometric Functions — Maths STD 11 Science — Question

CBSE BoardEnglish MediumSTD 11 ScienceMathsPART - 1 CH - 3 Trigonometric Functions2 Marks
Question
Prove that:
$
\begin{array}{l}
\sin (n+1) A \sin (n+2) A+\cos (n+1) A \cos (n+2) A=\cos A
\end{array}
$
✓

Answer


$\begin{array}{l}\text { L.H.S. }=\sin (n+1) A \sin (n+2) A+\cos (n+1) \\A \cos (n+2) A \\\Rightarrow \quad \cos (n+2) A \cos (n+1) A+\sin (n+2) A \sin (n+1) A \\\Rightarrow \quad \cos [(n+2) A-(n+1) A]= \cos [(n+2-n-1) A] \\=\cos A=RHS\end{array}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "2 Marks Questions" from PART - 1 CH - 3 Trigonometric Functions→PART - 1 CH - 3 Trigonometric Functions — all question types→Maths STD 11 Science question papers→CBSE Board STD 11 Science question papers→CBSE Board question paper generator→

Similar questions

Find the equation of the right bisector of the line segment joining the points (3, 4) and (-1, 2).
→
Find the general solutions of the following equations:
$\tan\text{x}=-\frac{-1}{\sqrt{3}}$
→
Let f = {(1, 1), (2, 3), (0, - 1), - 1, - 3)} be a function from Z to Z defined by f (x) = ax + b for some integers a, b. Determine a,b.
→
Find the number of $4-$digit numbers that can be formed using the digits $1, 2, 3, 4, 5$ if no digit is repeated. How many of these will be even?
→
Let A = {1, 2, 3}, B = {3, 4} and C = {4, 5, 6}. Find : (A $\times$ B) $\cup$ (A $\times$ C)
→
Let f = {(1, 1), (2, 3), (0, –1), (–1, –3)} be a linear function from Z into Z. Find f(x).
→
Show the following quadratic equation by factorization method:
$\text{x}^2-(2\sqrt{3}+3\text{i}))\text{x}+6\sqrt{3}\text{ i}=0$
→
Find the centre and radius of the circle. $x ^2 + y ^2 - 8x - 10y - 12 = 0$
→
Evaluate the following limit:
$\lim\limits_{\text{x}\rightarrow{\text{a}}}\frac{\cos\text{x}-\cos\text{a}}{\text{x}-\text{a}}$
→
Show the following quadratic equation by factorization method:
$x^2 + 10ix - 21 = 0$
→